Ink jet recording method, ultraviolet curable ink, and ink jet recording apparatus

ABSTRACT

Provided is an ink jet recording method including: discharging first ultraviolet curable ink of a radical polymerization reaction type which contains a radical photopolymerization initiator and a radical polymerization compound and in which transmittance at a wavelength of 395 nm is equal to or less than 1%, onto a recording medium; and curing the first ultraviolet curable ink which is landed on the recording medium by irradiating the ink with ultraviolet light, in which a light source which initially emits the ultraviolet light in the curing of the ink is an ultraviolet light emitting diode in which peak intensity of the irradiated ultraviolet light is equal to or more than 800 mW/cm 2 .

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/735,447, filed Jan. 6, 2020, which is a continuation of U.S. patentapplication Ser. No. 15/991,316, filed May 29, 2018 and granted on Feb.25, 2020 as U.S. Pat. No. 10,569,571, which is a division of U.S. patentapplication Ser. No. 15/373,390, filed Dec. 8, 2016 and granted on May29, 2018 as U.S. Pat. No. 9,981,486, which is a division of U.S. patentapplication Ser. No. 13/851,627, filed Mar. 27, 2013 and granted on Mar.27, 2018 as U.S. Pat. No. 9,925,801, which claims priority to JapanesePatent Application No. 2012-074298, filed Mar. 28, 2012, and JapanesePatent Application No. 2012-074293, filed Mar. 28, 2012. The entiredisclosures of the above-identified patent applications are expresslyincorporated by reference herein.

BACKGROUND 1. Technical Field

The present invention relates to an ink jet recording method, anultraviolet curable ink and an ink jet recording apparatus.

2. Related Art

In the related art, as a recording method for forming an image based onan image data signal on a recording medium such as paper, variousmethods have been used. Among them, since an ink jet method is used withan apparatus with a low cost which discharges ink only to a necessaryimage unit and performs direct image formation on a recording medium, itis possible efficiently to use the ink and to keep the running cost islow. Furthermore, since noises are small in the ink jet method, the inkjet method is excellent as a recording method.

In recent years, in order to form an image having excellent waterresistance, solvent resistance, rub fastness and the like on a surfaceof a recording medium, an ink jet recording method using ultravioletcurable ink which is cured when being irradiated with ultraviolet lighthas been used.

For example, JP-A-2010-131975 discloses a line recording type imageforming method of discharging a photoacid generator solution PI-1(CPI-100P manufactured by San-Apro Ltd., a photoacid generator solutionof sulfonium salt which is dissolved in propylene carbonate) onto arecording material in advance, subsequently irradiating the photoacidgenerator solution which is landed onto the recording material withultraviolet light from a metal halide lamp (VZero270 manufactured byIntegration Technology, the maximum illumination of 400 mW/cm²),discharging cationic polymerization-based active light curable ink (inorder of black, cyan, magenta, yellow and white) formed of a photoacidgenerator (photo radical generator is not used), a cationicpolymerization compound, a pigment dispersion, a surfactant and asensitizer, each of which has predetermined types and amountssequentially, to form an image, and then, performing irradiation withactive light from an LED (manufactured by Nichia Corporation, 365nm-multi chip array, a water cooling type, the maximum illumination of1,500 mW/cm²) to fix an image (Paragraphs [0028], [0088], [0094] to[0097], [0099] to [0101] (Table 1), and [0106], Sample No. 1 in Table 5in [0107], FIG. 1, and Paragraph [0112] in JP-A-2010-131975).

In addition, for example, International Publication No. WO 2011/039081discloses a recording method of discharging ultraviolet curable ink jetink consisting of 15% by weight of a dispersion liquid including C.I.Pigment Blue 15:4 which is a pigment, 62.55% by weight of propoxylatedneopentyl glycol diacrylate (SR9003), 13% by weight of 2-(2-vinyloxyethoxy) ethyl acrylate (VEEA), 0.83% by weight of a polymerizationinhibitor, 6% by weight of a photopolymerization initiator, 2.5% byweight of ethyl-4-(dimethylamino) benzoate, and 0.1% by weight ofpolyether-modified polydimethylsiloxane which is a wetting agent from aprint head in which density of nozzles and an outer diameter thereof areset as the predetermined values, and performing irradiation withultraviolet light (Example 1 in International Publication No. WO2011/039081).

However, when manufacturing a cured film, that is, a coating film ofcured ink, from ultraviolet curable ink jet ink using the image formingmethod which is disclosed in JP-A-2010-131975, the following problemsoccur.

When a coating film of ink is irradiated with ultraviolet light, apigment strongly tends to absorb a part of ultraviolet light, andaccordingly, although irradiation is performed with the ultravioletlight, an energy necessary for the complete curing of the coating filmwhich is discharged onto a recording medium, is insufficient, and thusthe vicinity of the surface of the coating film is initially cured, andthus, the inner portion of the coating film is incompletely cured ormore time is necessary for the curing, in some cases. In addition, whenthe uncured ink existing in the inner portion of the coating film iscured, wrinkles are generated on the vicinity of the surface of thecoating film which is initially cured, or by irregular flow of the inkbefore the ink in the inner portion of the coating film is cured,wrinkles (hereinafter, referred to as “cured wrinkles”) are generated onthe surface of the coating film after the curing. Due to the curedwrinkles, problems of degradation of various kinds of film properties onthe coating film occur. The thicker the film thickness of a cured film,the stronger such a tendency is.

In addition, when a cured film, in other words, a coating film of an inkwhich is cured, from an ultraviolet curable ink jet ink using arecording method which is disclosed in International Publication No. WO2011/039081, is attempted to be formed, problems occur as below.

Firstly, in a case where the film thickness of a cured film isrelatively thin, the hardenability is inferior due to the affects ofoxygen inhibition in a case of a radical polymerization reaction system.Therefore, the film has to be thickened in excess to the extent in whichoxygen inhibition does not occur when printing and a problem of theprinted image quality occurs where the image becomes very poor. On theother hand, in a case where the film thickness of a cured film isrelatively thick, there is a strong tendency that a pigment absorbs apart of ultraviolet light, and then, even if ultraviolet light isirradiated, the energy which is needed for completely curing the coatingfilm which is discharged onto a recording medium, becomes insufficient,therefore, there is a case where the curing of the inside of the coatingfilm becomes incomplete due to the vicinity of the surface of thecoating film being cured in first or there is a need to take time forcuring. Further, due to the vicinity of the surface which has been curedbefore wrinkles when an uncured ink which is present inside the coatingfilm is cured or an ink irregularly flowing before an ink inside thecoating film is cured, wrinkles (hereinafter also referred to as “curedwrinkles”) occur on the surface of the film coating after curing. Due tothe cured wrinkles, problems occur wherein film characteristics on thecoating film are inferior.

SUMMARY

Here, an advantage of some aspects of the invention is to provide an inkjet recording method capable of preventing generation of cured wrinkles.

In addition, another advantage of some aspects of the invention is tofurther provide ultraviolet curable ink which is used in the recordingmethod and an ink jet recording apparatus using the recording method.

Here, an advantage of some aspects of the invention is to provide an inkjet recording method which has excellent hardenability and in which itis possible to prevent the occurrence of cured wrinkles.

In addition, an advantage of some aspects of the invention is further toprovide an ultraviolet curable ink which is used in the recording methodand an ink jet recording apparatus using the recording method.

The present inventors have found that, when radical polymerizationreaction type ultraviolet curable ink (hereinafter also referred to as“first ultraviolet curable ink”) in which transmittance at a wavelengthof 395 nm is equal to or less than 1%, is discharged onto a recordingmedium and then, the ink is cured, by setting a light source whichinitially irradiates with ultraviolet light (first ultravioletirradiation) as an ultraviolet light emitting diode in which peakintensity (hereinafter also referred to as “irradiation peak intensity”)of the irradiated ultraviolet light is equal to or more than 800 mW/cm²,cured wrinkles can be efficiently prevented.

That is, a first invention is as described below.

[1] According to an aspect of the invention, there is provided an inkjet recording method, including: is charging first ultraviolet curableink of a radical polymerization reaction type which contains a radicalphotopolymerization initiator and a radical polymerization compound andin which transmittance at a wavelength of 395 nm is equal to or lessthan 1%, onto a recording medium; and curing the first ultravioletcurable ink which is landed on the recording medium by irradiating theink with ultraviolet light, wherein a light source which initially emitsthe ultraviolet light in the curing of the ink is an ultraviolet lightemitting diode in which peak intensity of the irradiated ultravioletlight is equal to or more than 800 mW/cm².

[2] The ink jet recording method according to [1], wherein anirradiation energy of the ultraviolet light emitted from the ultravioletlight emitting diode which initially emits ultraviolet light is 100mJ/cm² to 600 mJ/cm².

[3] The ink jet recording method according to [1] or [2], furtherincluding further emitting ultraviolet light, after emitting ultravioletlight from the ultraviolet light emitting diode which is a light sourcewhich initially emits the ultraviolet light.

[4] The ink jet recording method according to any one of [1] to [3],wherein the irradiation from the ultraviolet light emitting diode whichinitially emits the ultraviolet light is at least any of pulseirradiation and spot irradiation by a condensing lens.

[5] The ink jet recording method according to any one of [1] to [4],further including recording using a line type ink jet recordingapparatus including discharging the first ultraviolet curable ink ontothe recording medium, while relatively moving positions of a headincluding nozzle arrays having a length equal to or greater than alength corresponding to a width of the recording medium and therecording medium in a scanning direction intersecting the widthdirection.

[6] The ink jet recording method according to any one of [1] to [5],wherein peak intensity of ultraviolet light emitted from the ultravioletlight emitting diode which initially emits the ultraviolet light is in arange of 800 mW/cm² to 4000 mW/cm².

[7] The ink jet recording method according to any one of [1] to [6],wherein the ultraviolet light emitting diode which initially emitsultraviolet light has a light emitting peak wavelength in a range of 360nm to 420 nm.

[8] The ink jet recording method according to any one of [1] to [7],further including: discharging second ultraviolet curable ink of aradical polymerization reaction type which contains a radicalphotopolymerization initiator and a radical polymerization compound andin which transmittance at a wavelength of 395 nm exceeds 1%, onto arecording medium; and curing the second ultraviolet curable ink which islanded on the recording medium by irradiating the ink with ultravioletlight, wherein a light source which initially emits ultraviolet light inthe curing of the ink is an ultraviolet light emitting diode in whichpeak intensity of the irradiated ultraviolet light is less than 800mW/cm².

[9] The ink jet recording method according to [8], further including:discharging the first ultraviolet curable ink onto a recording medium;curing the first ultraviolet curable ink which is landed on therecording medium by irradiating the ink with ultraviolet light;discharging the second ultraviolet curable ink onto a recording medium;curing the second ultraviolet curable ink which is landed on therecording medium by irradiating the ink with ultraviolet light; andfurther curing the first ultraviolet curable ink and the secondultraviolet curable ink by irradiating the ink with ultraviolet light.

[10] The ink jet recording method according to [8] or [9], wherein thedischarging of the first ultraviolet curable ink onto the recordingmedium and the curing the first ultraviolet curable ink which is landedon the recording medium by irradiating the ink with ultraviolet lightare performed after the discharging of the second ultraviolet curableink onto a recording medium and the curing the second ultravioletcurable ink which is landed on the recording medium by irradiating theink with ultraviolet light.

[11] An ultraviolet curable ink used in the ink jet recording methodaccording to any one of [1] to [10].

[12] An ink jet recording apparatus which is used with the ink jetrecording method according any one of [1] to [10].

In addition, the present inventors have found that, when dischargingultraviolet curable ink containing predetermined vinyl ethergroup-containing (meth)acrylate esters onto a recording medium, and thencuring the ink, by emitting ultraviolet light from an ultraviolet lightemitting diode in which peak intensity of the irradiated ultravioletlight (hereinafter, also referred to as “irradiation peak intensity”) isequal to or more than 800 mW/cm², excellent hardenability can beobtained for a recorded material to be obtained, and cured wrinkles canbe efficiently prevented.

That is, a second invention is as described below.

[1] According to another aspect of the invention, there is provided anink jet recording method including: discharging ultraviolet curable inkcontaining vinyl ether group-containing (meth)acrylate esters expressedby the following General Formula (I) onto a recording medium; and curingthe ultraviolet curable ink which is landed on the recording medium byirradiating the ink with ultraviolet light from an ultraviolet lightemitting diode in which peak intensity of the irradiated ultravioletlight is equal to or more than 800 mW/cm².

CH₂═CR¹—COOR²—O—CH═CH—R³  (I)

(In the formula, le represents a hydrogen atom or a methyl group, R²represents a divalent organic residue having 2 to 20 carbon atoms, andR³ represents a hydrogen atom or a monovalent organic residue having 1to 11 carbon atoms.)

[2] The ink jet recording method according to [1], wherein anirradiation energy of ultraviolet light emitted from the ultravioletlight emitting diode is 100 mJ/cm² to 600 mJ/cm².

[3] The ink jet recording method according to [1] or [2], furtherincluding preliminarily curing the ultraviolet curable ink byirradiating the ink with ultraviolet light in which an irradiationenergy is equal to or less than 50 mJ/cm² from an ultraviolet lightemitting diode generating ultraviolet light in which a light emittingpeak wavelength is in a range of 360 nm to 420 nm and peak intensity ofthe irradiated ultraviolet light is less than 800 mW/cm², beforeirradiating the ink with ultraviolet light from an ultraviolet lightemitting diode in which the peak intensity is equal to or more than 800mW/cm², in the curing of the ink.

[4] The ink jet recording method according to any one of [1] to [3],further including recording using a line ink jet recording apparatusincluding a line head having a length equal to or greater than a lengthcorresponding to a width of a recording medium.

[5] The ink jet recording method according to any one of [1] to [4],wherein the irradiation from the ultraviolet light emitting diode is atleast any of pulse irradiation and spot irradiation by a condensing lensindividually.

[6] The ink jet recording method according to [1] or [2], wherein peakintensity of the irradiated ultraviolet light is in a range of 800mW/cm² to 4000 mW/cm².

[7] The ink jet recording method according to [1] or [2], wherein theultraviolet light emitting diode has a light emitting peak wavelength ina range of 360 nm to 420 nm.

[8] An ultraviolet curable ink used for the ink jet recording methodaccording to any one of [1] to [7].

[9] An ink jet recording apparatus which is used with the ink jetrecording method according to any one of [1] to [7].

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a block diagram showing a configuration of a line printer.

FIG. 2 is a schematic view of a recording area periphery in oneembodiment of a line printer in FIG. 1.

FIG. 3 is a sectional view schematically showing a part of an example ofa lens-attached UV-LED among first irradiation units.

FIG. 4 is a schematic view of a recording area periphery in anotherembodiment of a line printer in FIG. 1.

FIG. 5A is a waveform chart of pulse current which flows to an UV-LED ina printer in one embodiment of the invention in a case of not performingpulse irradiation with ultraviolet light.

FIG. 5B is a waveform chart of pulse current which flows to an UV-LED ina printer in one embodiment of the invention in a case of performingpulse irradiation with ultraviolet light.

FIG. 6 is a schematic view of a head periphery of a serial printer.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, embodiments of a first invention will be described indetail. The invention is not limited to the following embodiments, andvarious modifications can be performed in a range not departing from thegist of the invention. In addition, in each drawing used in thefollowing description, scale of each constituent element (member) isappropriately changed for a size of each constituent element to bevisually recognized on the drawings. The embodiments are not onlylimited to a ratio of quantity, a shape and a size of the constituentelements and a relative positional relationship of each constituentelement described in the drawings.

In the present specification, a “hardenability” refers to a property forcuring by photoresponse. “Cured wrinkles” mean wrinkles which aregenerated on a surface of a coating film after curing, as a result ofincrease of a coefficient of polymerization volumetric shrinkage byirregular flow of uncured ink existing in the coating film which is atarget of curing, before curing, as described above. “Abrasionresistance” refers to a property in which it is difficult for a curedmaterial to be peeled off and to be scratched when the cured material isrubbed.

In this specification, “discharging stability” refers to a propertywhich is to be able to discharge ink droplets which are always stablewithout clogging of a nozzle, from a nozzle. “Bleed” means bleeding and“bleed resistance property” refers to a property in which bleedinghardly occurs on the edge of an image. “Uneven brightness” means thatthe difference in shiny appearance between these patterns is seen whenan ink pattern which is discharged at first and an ink pattern which isdischarged next are adjacently formed. “Preservation stability” refersto a property wherein the viscosity before and after storage is hardlychanged when an ink is stored.

In this specification, a “pixel” means the minimum recording unit areacorresponding to recording resolution.

In the specification, “(meth)acrylate” means at least any of acrylateand methacrylate corresponding thereto, “(meth)acryl” means at least anyof acryl and methacryl corresponding thereto, and “(meth)acryloyl” meansat least any of acryloyl and methacryloyl corresponding thereto.

Ink Jet Recording Apparatus

One embodiment of the invention relates to an ink jet recordingapparatus, that is, a printer. The recording apparatus is used with anink jet recording method which will be described later. FIG. 2 is aschematic view of a recording area circumference in one aspect of a lineprinter.

As types of the printer in the embodiment, a line printer and a serialprinter are used, and any of these can be used. The printers are usedwith different printer system. A line printer which is an ink jetrecording apparatus of a line system (line type) is a line printer whichdischarges the ink onto a recording medium, while relatively movingpositions of a head including nozzle arrays having a length greater thana length corresponding to a width of the recording medium and therecording medium in a scanning direction intersecting the widthdirection, and the head is (substantially) not moved, and is fixed, andthe recording is performed with one pass (single pass). On the otherhand, a serial printer which is an ink jet recording apparatus with aserial system is a serial printer which normally performs recording bytwo or more passes (multi passes) while reciprocating (shuttle movement)of a head in a direction orthogonal to a transportation direction of arecording medium. Here, the length of the nozzle array is preferable aslong as it is a length (almost) corresponding to a width of a recordingmedium, however, the length of the nozzle row is preferable to be alength equal to or greater than a length corresponding to a width of arecording medium, and is more preferable to be a length corresponding toa width of a recording medium.

Among these, since the serial printer has a pixel in which the ink isnot discharged with one pass, or has adjacent pixels in which the ink isnot discharged, an ink discharge amount per one pass is relativelysmall. Accordingly, in a serial printer, there is a tendency in whichcured wrinkles are hardly generated, and meanwhile, a recording rate islow due to recording by multi passes or the like. On the other hand, aswill be described later, a line printer is a printer which forms animage only by single scanning of a recording medium in a predetermineddirection (hereinafter, referred to as “transportation direction”).Accordingly, a line printer is preferable from a viewpoint of asignificantly high recording rate, compared to a serial printer,however, problems in that an ink discharge amount per one pass is largeand cured wrinkles are easily generated occur. Here, the embodimentcapable of preventing generation of cured wrinkles is not limited to aline printer, however, significant effects are particularly exhibitedwith respect to a line printer. Hereinafter, a line printer will bedescribed with reference to FIG. 1 and FIG. 2.

A printer 1 is a recording apparatus which forms an image on a recordingmedium and is communicatively connected to a computer 110 which is anexternal apparatus.

A printer driver is installed in the computer 110. The printer driver isa program for displaying a user interface to a display device (notshown) to convert image data output from an application program intorecording data (image forming data). The printer driver is recorded in a“computer-readable recording medium” such as a flexible disk (FD) or aCD-ROM. Alternatively, the printer driver can be downloaded to thecomputer 110 through Internet. In addition, the program is configuredfrom a code for realizing various functions.

In order to form an image by the printer 1, the computer 110 outputsrecording data corresponding to the image to the printer 1.

Here, the “recording apparatus” of the present specification means anapparatus which forms an image on a recording medium, and for example,corresponds to the printer 1. In addition, a “recording controllingapparatus” means an apparatus which controls a recording apparatus, andfor example, corresponds to the computer 110 in which the printer driveris installed.

The printer 1 of the embodiment is an apparatus which forms an image ona recording medium by discharging predetermined ultraviolet curable inkwhich is cured by irradiation with ultraviolet light. As thepredetermined ultraviolet curable ink, at least first ultravioletcurable ink is used. The predetermined ultraviolet curable ink containsat least a radical photopolymerization initiator and a radicalpolymerization compound, and is cured by polymerization reaction due toirradiation with ultraviolet light.

A detailed ink composition of the ultraviolet curable ink will bedescribed later.

The printer 1 of the embodiment includes a transportation unit 20, ahead unit 30, an irradiation unit 40, a detector group 50, and acontroller 60. The printer 1 which received recording data from thecomputer 110 which is an external apparatus controls each unit, that is,the transportation unit 20, the head unit 30, and the irradiation unit40, by the controller 60, and forms an image on a recording medium Saccording to recording data. The controller 60 controls each unit andforms an image on the recording medium S, based on recording datareceived from the computer 110. The state in the printer 1 is monitoredby the detector group 50, and the detector group 50 outputs a detectionresult to the controller 60. The controller 60 controls each unit, basedon the detection result output from the detector group 50.

The transportation unit 20 is a unit which transports the recordingmedium S in a transportation direction. As shown in FIG. 2, thetransportation unit 20 includes an upstream transportation roller 23A, adownstream transportation roller 23B, and a belt 24, for example. Whenrotating the transportation roller (not shown), the upstreamtransportation roller 23A and the downstream transportation roller 23Bare rotated, and the belt 24 is rotated. The recording medium S which isfed by a paper feeding roller (not shown) is transported to a recordablearea (area opposing to the head), by the belt 24. By transporting therecording medium S by the belt 24, the recording medium S is moved withrespect to the head unit 30 in the transportation direction. Therecording medium S which passes the recordable area is discharged tooutside by the belt 24.

In addition, the recording medium S which is being transported iselectrostatic-adsorbed or vacuum-adsorbed to the belt 24. Herein, aphrase of “paper feeding” is used for convenience sake, however, as therecording medium of the embodiment, recording media which will bedescribed later can be used.

The head unit 30 is for discharging the ultraviolet curable ink to therecording medium S. By discharging each ink with respect to therecording medium S which is being transported, the head unit 30 formsdots on the recording medium S and forms an image. The printer 1 of theembodiment is a line printer, each head of the head unit 30 (almost)corresponds to a length of a width of the recording medium, and a dotgroup corresponding to the width can be formed at one time. In detail,as shown in FIG. 2 which is a schematic view of the recording areaperiphery of an aspect of the line printer in FIG. 1, in a case whereeach head of a white ink head W, a black ink head K, a cyan ink head C,a magenta ink head M, and a yellow ink head Y is provided in order fromupstream of the transportation direction, a plurality of heads aredisposed so that each head can discharge dot groups corresponding to thewidth of the recording medium S in a front direction from the back of apaper surface. As described above, by controlling each head from theupstream and forming dots in a necessary location in one linecorresponding to the width of the recording medium S, it is possible toform an image with only single scanning of the recording medium S in atransportation direction.

In addition, the white ink head W is a discharge unit of ultravioletcurable white ink. The black ink head K is a discharge unit ofultraviolet curable black ink. The cyan ink head C is a discharge unitof ultraviolet curable cyan ink. The magenta ink head M is a dischargeunit of ultraviolet curable magenta ink. The yellow ink head Y is adischarge unit of ultraviolet curable yellow ink.

The irradiation unit 40 irradiates the dots of ultraviolet curable inkwhich is landed on the recording medium S with ultraviolet light. Thedots formed on the recording medium S are cured by receiving emission ofthe ultraviolet light from the irradiation unit 40. As shown in FIG. 2,the irradiation unit 40 of the embodiment may include first irradiationunits 42 a to 42 e and a second irradiation unit 44.

The first irradiation unit 42 a to 42 e are for irradiating withultraviolet light for curing the dots formed on the recording medium,and are positioned before the second irradiation unit 44 which performscuring in the same manner, that is, upstream of the transportationdirection.

The first irradiation units 42 a to 42 e are provided on downstream ofthe transportation directions of the white ink head W, the black inkhead K, the cyan ink head C, the magenta ink head M, and the yellow inkhead Y, respectively. That is, the first irradiation units are providedfor each ink color.

Herein, the first ultraviolet curable ink which is necessary as ink ofthe embodiment is ink which satisfies conditions of transmittance whichwill be described later, and in detail, one or more types selected froma group consisting of yellow ink, black ink, orange ink, and green ink,can be obtained. Meanwhile, one or more types selected from a groupconsisting of white ink, cyan ink, magenta ink, and clear ink can be setink other than the first ultraviolet curable ink. In addition, in a casewhere two or more types of ink are discharged from the various ink, itis acceptable as long as at least one type thereof is the firstultraviolet curable ink, and the other ink may not be the firstultraviolet curable ink.

In addition, for example, as shown in FIG. 2, black ultraviolet curableink discharged from the black ink head K is irradiated with ultravioletlight by at least any of the first irradiation units 42 b to 42 e andthe second irradiation unit 44. At that time, the irradiation unit(light source) which initially irradiates the black ultraviolet curableink with ultraviolet light is an ultraviolet light emitting diode(UV-LED) having irradiation peak intensity of equal to or more than 800mW/cm². Accordingly, when the black ultraviolet curable ink isirradiated with ultraviolet light from the first irradiation units 42 band 42d and the second irradiation unit 44, the first irradiation unit42 b is necessary to be an UV-LED having irradiation peak intensity ofequal to or more than 800 mW/cm², and types or irradiation peakintensity of the other irradiation units, that is, the first irradiationunit 42 d and the second irradiation unit 44 are not particularlylimited. In addition, in this case, in a case of not emittingultraviolet light from the first irradiation unit 42 b, the firstirradiation unit 42 d which is an initial light source which performsirradiation is necessary to be an UV-LED which satisfies the aboveconditions.

The first irradiation units 42 a to 42 e include UV-LEDs as lightsources of ultraviolet irradiation. By controlling an amount of inputcurrent by the UV-LEDs, it is possible to easily change an irradiationenergy. Among the UV-LEDs, particularly the irradiation unit (lightsource) which initially irradiates the first violet curable ink withultraviolet light is preferable to be a type including a condensing lens(hereinafter, also referred to as a “lens-attached LED”), and byirradiating by condensing light to a limited area from the lens-attachedLED, it is possible to maintain an irradiation energy and to performspot irradiation with greater irradiation peak intensity. In addition,the irradiation units other than the irradiation unit which initiallyirradiates the ink with ultraviolet light may be or may not belens-attached LEDs.

Hereinafter, the lens-attached LED will be described. FIG. 3 is across-sectional view schematically showing a part of an example of thelens-attached UV-LED, from the first irradiation unit.

An UV-LED 72 is mainly configured by an UV-LED chip 72 a and acondensing lens 72 b which emits ultraviolet light, and ultravioletlight which is issued by the UV-LED chip 72 a is condensed by thecondensing lens 72 b to form a given irradiation angle and emitted to alower portion of the first irradiation unit. The condensing lens 72 b isa package which covers the UV-LED chip 72 a, is formed of a lens formedon the surface thereof in a hemispherical shape and a cover protectingthe surface thereof, and condenses ultraviolet light issued from theUV-LED chip 72 a towards a center line of a hemisphere. A material ofthe lens or the cover is not limited as follows, however, for example,transparent resin such as glass, silicon resin, silicon rubber, and thelike can be used. The structure of the lens is not limited to the abovedescribed structure as long as the light condensing can be performed,and for example, may be a structure where an attached lens which isseparately formed in a hemispherical shape, other than a lens which isformed in a hemispherical shape integrated with the package. The UV-LEDchip 72 a included in the irradiation unit 40 controls a supply currentvalue by an UV-LED driving circuit (not shown) controlled by thecontroller 60, can rapidly switch an on state and an off state, and canemit ultraviolet light having irradiation intensity necessary for curingthe uncured ultraviolet curable ink which is landed on the recordingmedium S. In addition, a plurality of UV-LED units including the UV-LEDare arranged in a line in the width direction and the transportationdirection of the recording medium S, and configure each firstirradiation unit. The positioning of the UV-LEDs arranged in a line inthe transportation direction of the recording medium S in directions ofthe UV-LEDs arranged in a line in the width direction of the recordingmedium S, in a viewpoint of even dispersion of irradiation areas wherethe light condensed from the UV-LEDs in the width direction of therecording medium S. In addition, the other configurations regarding theUV-LED units may be referred to FIG. 4 disclosed in JP-A-2010-23285, anddescription thereof, for example. Further, the irradiation energy, alight emitting peak wavelength, and irradiation beam intensity forcuring by the first irradiation units 42 a to 42 e will be describedlater.

The second irradiation unit 44 irradiates the dots formed on therecording medium S with ultraviolet light for curing the dots. Thesecond irradiation unit 44 is provided on downstream with respect to theyellow ink head Y in the transportation direction. In addition, a lengthof the second irradiation unit 44 in the width direction of therecording medium S is greater than a width of the recording medium S.The second irradiation unit 44 irradiates dots formed by each head ofthe head unit 30 with ultraviolet light.

The second irradiation unit 44 of the embodiment includes an UV-LED as alight source of ultraviolet irradiation. Since the UV-LED has beendescribed in the description of the first irradiation units 42 a to 42e, the description thereof will be omitted herein.

In addition, an irradiation energy, a light emitting peak wavelength,and irradiation peak intensity by the second irradiation unit 44 will bedescribed later.

A rotary encoder (not shown), a paper detecting sensor (not shown), andthe like are included in the detector group 50. The rotary encoderdetects rotation of the upstream transportation roller 23A or thedownstream transportation roller 23B. It is possible to detect atransportation amount of the recording medium S based on the detectionresults of the rotary encoder. The paper detecting sensor detects aposition of an end of the recording medium S which is being fed.

The controller 60 is a control unit which controls the printer. Thecontroller 60 includes an interface unit 61, a CPU 62, a memory 63, anda unit control circuit 64. The interface unit 61 performs transmissionand reception of data between the computer 110 which is an externalapparatus and the printer 1. The CPU 62 is an arithmetic processing unitwhich controls the entire printer. The memory 63 is a memory forsecuring an area for storing programs of the CPU 62 or operation areas,and includes memory elements such as RAM, EEPROM, and the like. The CPU62 controls each unit through the unit control circuit 64, according toprograms stored in the memory 63.

Modification Example of Ink Jet Recording Apparatus

The printer 1 of FIG. 1 described above is only an example of the inkjet recording apparatus according to the embodiment, and there are a lotof variations.

First, in FIG. 2, when the first ultraviolet curable black ink isdischarged from the black ink head K, light sources other than the lightsource (irradiation unit) which initially irradiates the firstultraviolet curable ink with ultraviolet light, that is, light sourceswhich position downstream with respect to the initial light source maybe or may not be exist. In a case where the light sources positioneddownstream exist, the light sources are not particularly limited, andother LED or a lamp such as a metal halide lamp, a xenon lamp, acarbon-arc lamp, a chemical lamp, a low-pressure mercury lamp, and ahigh-pressure mercury lamp may be used, other than the UV-LED.

The irradiation by the lamp is performed to an inner portion since alight emitting wavelength of a short wavelength is included, and thus,the cured wrinkles are hardly generated, and it is substantially notnecessary to initially have irradiation intensity of equal to or morethan 800 mW/cm². Meanwhile, problems occur in various points such asheat generation, size (including cooling device), power consumption, andlife time of the light source, and cost of the irradiator.

On the other hand, the ultraviolet irradiation by the UV-LED has aproblem in that cured wrinkles is easily generated compared to therelated art, however, the ink jet recording apparatus of the embodimentand the ink jet recording method of an embodiment which will bedescribed later is obtained by solving the problem of easy generation ofcured wrinkles. In addition, compared to the lamps described above, theUV-LED is small in size, has a long life time, less heat generation, andhigh efficiency, and is also excellent in a viewpoint of suppressingcost. Accordingly, in a case of performing ultraviolet irradiation usingthe UV-LED, the ink jet recording apparatus or the ink jet recordingmethod particularly realizes significant effects.

The above points are the same as in a case of discharging firstultraviolet curable yellow ink from the yellow ink head Y.

In addition, the order of the ink heads of each color shown in FIG. 2may be changed in any order, and only one ink head may be included orone or more ink heads which are not operated may be included. Further,the other ink heads (the colors may be the same as the existing inkheads or may be different) may be included in addition to the ink headsof each color shown in FIG. 2, or any of the ink heads may be changed tothe ink heads of other colors.

Hereinafter, concretization of various variations of the embodiment willbe described as Modification Examples, however, the embodiment is notparticularly limited to Modification Examples.

A recording apparatus according to First Modification Example is aprinter 1 including one or more heads and first irradiation unitspositioned downstream thereof in the transportation direction, from thewhite ink head W, the black ink head K, the cyan ink head C, the magentaink head M, and the yellow ink head Y, and the first irradiation units42 a to 42 e positioned downstream of each head in the transportationdirection. FIG. 4 shows an aspect of the First Modification Example, andis a schematic view of the vicinity of the recording areas of the otheraspect of the line printer of FIG. 1. The line printer shown in FIG. 1includes a head 45, a first irradiation unit 42 f, and the secondirradiation unit 44, from the upstream in the transportation direction.

In addition, the printer 1 of First Modification Example may not includethe second irradiation unit 44 or may include the second irradiationunit 44 which is not operated.

A recording apparatus according to Second Modification Example is arecording apparatus including the white ink head W, an irradiation unitfor white ink, the cyan ink head C, an irradiation unit for cyan ink,the magenta ink head M, an irradiation unit for magenta ink, the blackink head K, an irradiation unit which initially irradiates the black inkwhich is the first ultraviolet curable ink with ultraviolet light, theyellow ink head Y, an irradiation unit which initially irradiates theyellow ink which is the first ultraviolet curable ink with ultravioletlight, an clear ink head CL, and an irradiation unit for clear ink, fromthe upstream in transportation direction. According to the recordingapparatus according to Second Modification Example, it is possible torealize an excellent shielding property by setting the white ink as abase, and quality improvement of an image by overcoating the clear ink(transparent ink). In addition, before and after discharging the clearink from the clear ink head CL, by emitting ultraviolet light from eachirradiation unit, it is possible to perform proper curing of the colorink before discharging the clear ink.

In addition, the recording apparatus according to Second ModificationExample may not include at least any of the white ink head W, theirradiation unit for white ink, and the clear ink head CL.

A recording apparatus according to Third Modification Example includesan UV-LED not including a condensing lens (hereinafter, also referred toas an “LED with no lens”) as an UV-LED which is an irradiation source ofultraviolet light, instead of the lens-attached LED. The LED with nolens has the same configuration as in the case of the lens-attached LED,except for a point of not including the condensing lens 72 b of FIG. 3.An example of the LED with no lens is formed on a flat surface, otherthan on the surface of the package covering the UV-LED chip 72 a of FIG.3 in a hemispherical shape, and a cover protecting the surface thereofis also formed on a flat surface.

A recording apparatus according to Fourth Modification Example is arecording apparatus which performs pulse irradiation with ultravioletlight by setting input current to LEDs of at least any of the firstirradiation units 42 a to 42 e and the second irradiation unit 44 aspulse current by repeatedly switching the on state and the off state bythe UV-LED driving circuit (not shown) (herein, the LED is also referredto as “pulse irradiation LED”). As a driving circuit of the pulseirradiation LED, an MOF SET circuit or the like which performs PWMcontrol can be used. FIG. 5A is a waveform chart of current which flowsto the UV-LED in a printer of the embodiment, in a case of notperforming pulse irradiation with ultraviolet light. FIG. 5B is awaveform chart of pulse current which flows to the UV-LED in a printerof the embodiment, in a case of performing pulse irradiation withultraviolet light. In a case of the pulse current, the input current ispulse peak current, that is, peak input current. The total electricenergy input to the UV-LED is calculated with the following expression.

Total electric energy=input current×T1×Duty ratio

In the expression, T1 means irradiation time for the recording medium,and time from start of irradiation of the recording medium to the end ofthe irradiation. Duty ratio is a value expressed in the followingexpression when performing 1 periodic driving of pulse.

Duty ratio=duration when current is turned on/(duration when current isturned on+duration when current is turned off)

A Duty ratio of the LED which does not perform the pulse irradiationis 1. A Duty ratio in a case of performing the pulse irradiation may be0.5, for example, and a pulse frequency may be set as 1 kHz, forexample. Heat generation of the UV-LED generally becomes greater as thetotal electric energy becomes greater.

The irradiation peak intensity of the UV-LED generally becomes greateras the input current becomes greater. By performing the pulseirradiation as shown in FIG. 5B, in a case of fixing time T1 from thestart of the irradiation to the end of the irradiation, it is possibleto have greater irradiation peak intensity while maintaining the totalinput current. As described above, since the pulse irradiation LEDefficiently increase the irradiation peak intensity, it is particularlysuitable to be used for the first irradiation unit 42 in which greaterirradiation peak intensity is necessary.

For example, FIG. 1, FIG. 2, and the description thereof disclosed inJP-A-2006-231795, and description disclosed in JP-T-2011-523370 may bereferred for the pulse irradiation LED described above. The irradiationenergy of the pulse irradiation LED can be calculated using thefollowing expression.

Irradiation energy=irradiation peak intensity×T1×Duty ratio

Accordingly, when T1 is fixed, it is possible to increase the peakintensity while maintaining the same irradiation energy of the LED or itis possible to decrease the irradiation energy of the LED whilemaintaining the same peak intensity, in a case of performing the pulseirradiation, compared to the case of not performing the pulseirradiation.

In addition, the irradiation from UV-LED is preferable to be at leastany of the pulse irradiation and the spot irradiation. In this case, asdescribed above, it is possible to further increase the irradiation peakintensity while maintaining the irradiation energy.

A recording apparatus according to Fifth Modification Example is arecording apparatus which uses a serial printer instead of the lineprinter described with reference to FIG. 2 and the like. Characteristicsof the line printer and the serial printer are as described above.Hereinafter, an example of the serial printer will be briefly described.FIG. 6 is a schematic view of the vicinity of the head of the serialprinter.

A carriage unit 80 is a movement mechanism which moves, that is, scans ahead 85 with respect to a recording medium rested in a recording area,in a direction (hereinafter, referred to as a “moving direction” or a“main scanning direction”) intersecting the transportation direction(auxiliary scanning direction), while discharging ink. The carriage unit80 includes a carriage 81 and a carriage motor (not shown). In addition,the carriage 81 detachably holds an ink carriage (not shown) whichaccommodates ultraviolet curable ink. The carriage 81 reciprocates alonga guide spindle 82 by the carriage motor, in a state of being supportedby the guide spindle 82 which intersects the transportation directionwhich will be described later.

The head 85 is for discharging ultraviolet curable ink with respect to arecording medium, and includes a plurality of nozzles. Since the head 85is provided in the carriage 81, when the carriage 81 is moved in themoving direction, the head 85 also moves in the moving direction. Byintermittently discharging ultraviolet curable ink by the head 85 whichis being moved in the moving direction, dot rows along the movingdirection are formed on the recording medium.

In addition, in the movement of the head 85, the discharging of theultraviolet curable ink is performed during movement from one end sideto the other end side of FIG. 6, however the discharging of theultraviolet curable ink is not performed during movement from the otherend side to the one side.

The irradiation unit 90 irradiates the ultraviolet curable ink which isattached (landed) on the recording medium with ultraviolet light to curethe ultraviolet curable ink. The dots formed on the recording medium isirradiated with ultraviolet light from the irradiation unit 90 to becured, and a cured material is formed. The irradiation unit 90 includesfirst irradiation units 92 a and 92 b and a second irradiation unit 93on downstream of the head 85 in the transportation direction.

Herein, the first irradiation units 92 a and 92 b correspond to thefirst irradiation units of the line printer described above, and thesecond irradiation unit 93 corresponds to the second irradiation unit ofthe line printer described above. In the configuration and the operationof the serial printer, the irradiation unit which initially irradiatesfirst ultraviolet curable ink from the first irradiation units 92 a and92 b corresponds to a light source which initially irradiates the firstultraviolet curable ink with ultraviolet light.

In addition, detailed description of other points regarding the firstirradiation units 92 a and 92 b and the second irradiation unit 93 willbe omitted.

One unit recording operation is realized with one main scanning by thecarriage unit 80, the head 85, the first irradiation units 92 a and 92b, and the second irradiation unit 93, and in the embodiment, the unitrecording operations are performed plural times. Herein, the “unitrecording operation” means a single operation of forming an image overthe entire recording medium, and is also referred to as a pass or mainscanning.

When performing the recording, a dot formation operation of dischargingultraviolet curable ink from the head 85 which is being moved in themoving direction, and a transportation operation of transporting arecording medium in the transportation direction are alternatelyrepeated, and an image formed of a plurality of dots is recorded on therecording medium.

An ink jet recording method using the serial printer includes performingthe unit recording operation (unit recording step) plural times, whichincludes at least a discharging step of discharging ultraviolet curableink from the head 85 towards a recording medium, and a curing step ofirradiating ultraviolet curable ink which is landed on a recordingmedium with ultraviolet light to cure the ultraviolet curable ink. Inmore detail, the recording method is a method of performing recording byalternately performing the unit recording operation and thetransportation operation (transporting step) of transporting a recordingmedium. Accordingly, when recording, the recording medium is nottransported, and is in a state of being held by a platen (not shown)which positions in the recording area. Thus, it is possible to form acured material in an area of the recording medium opposing to the head85.

In addition, when performing the recording of the ink set using theserial printer with different irradiation peak intensity for initialirradiation depending on each ink after the discharging, as shown inFIG. 2 in JP-A-2011-25684, for example, the recording may be performedusing a serial printer including a light source for each head of thecarriage.

Ink Jet Recording Method

One embodiment of the invention relates to an ink jet recording method.The ink jet recording method can be performed using the ink jetrecording apparatus of the embodiment described above. In addition, theink jet recording method includes a discharging step of dischargingfirst ultraviolet curable ink of a radical polymerization reaction typewhich contains a radical photopolymerization initiator and a radicalpolymerization compound and in which transmittance at a wavelength of395 nm is equal to or less than 1%, onto a recording medium, and acuring step of curing the first ultraviolet curable ink which is landedon the recording medium by initially irradiating the ink withultraviolet light from an UV-LED in which irradiation peak intensity isequal to or more than 800 mW/cm².

Discharging Step

In the discharging step, viscosity of the ink at the time of beingdischarged is preferable to be equal to or less than 25 mPa·s, and morepreferable to be 5 mPa·s to 20 mPa·s. If the viscosity of the ink is asdescribed above when a temperature of the ink is a room temperature orin a state of not heating the ink, the ink may be discharged with atemperature of the ink as a room temperature or without heating the ink.Meanwhile, by heating the ink to a predetermined temperature, the inkmay be discharged by setting the viscosity to a preferable value.Accordingly, excellent discharging stability is realized.

Since ultraviolet curable ink has high viscosity than water-based inkused for ink for normal ink jet, viscosity fluctuation due totemperature fluctuation at the time of discharging is large. Suchviscosity fluctuation of the ink largely affects change of liquiddroplet size and change of liquid droplet discharging speed, andfurther, image quality degradation may occur. Accordingly, it ispreferable to maintain a constant temperature of the ink at the time ofdischarging as much as possible.

Curing Step

Next, in the curing step, first ultraviolet curable ink which isdischarged onto and landed on the recording medium is cured by initiallyreceiving ultraviolet irradiation from any UV-LED having irradiationpeak intensity of equal to or more than 800 mW/cm² from the firstirradiation units 42 a to 42 e and the second irradiation unit 44. Inother words, an ink coating film formed on the recording medium becomesa cured film by the irradiation with ultraviolet light. This is becausethat at least the radical photopolymerization initiator included in thefirst ultraviolet curable ink is decomposed by the irradiation withultraviolet light to generate radical which is an initiating species,and polymerization reaction of the radical polymerization compound ispromoted by functions of the radical. Alternatively, it is because thatthe radical polymerization reaction of the radical polymerizationcompound starts by the irradiation with ultraviolet light. At that time,if there is at least a sensitizing dye with the radicalphotopolymerization initiator in the first ultraviolet curable ink, thesensitizing dye in a system absorbs active ultraviolet light to be in anexcitation state, and promotes the decomposition of the radicalphotopolymerization initiator by being in contact with the radicalphotopolymerization initiator, and it is possible to realize curingreaction with higher sensitivity.

The predominance for using the UV-LED as the light source is asdescribed above.

The light emitting peak wavelength at the time of the irradiation ispreferable to be in a range of 360 nm to 420 nm, and more preferable tobe in a range of 380 nm to 410 nm. It is suitable that the lightemitting peak wavelength be in the range described above, fromviewpoints of easy purchase and low cost of the UV-LED.

In addition, the light emitting wavelength may be one or more in thepreferable wavelength range. Even in a case of the plurality of lightemitting peak wavelength, the entire irradiation energy amount ofultraviolet light having the light emitting peak wavelength in the abovedescribed range is set as the irradiation energy described above.

The peak intensity (irradiation peak intensity) of the ultraviolet lightinitially emitted to the first ultraviolet curable ink is equal to ormore than 800 mW/cm², and preferably equal to or more than 1000 mW/cm².If the irradiation peak intensity is in the range described above,hardenability is excellent, and it is possible to effectively preventgeneration of cured wrinkles. In more detail, as a result of delay ofthe curing of the inner portion of the ink coating film compared to thecuring of the surface thereof, the surface of the ink coating film isfirst cured, and it is possible to effectively prevent generation ofcured wrinkles.

The irradiation peak intensity will be further described. The LEDs havenarrow range of the light emitting wavelength from the characteristicsthereof, and among them, as described above, the long-wavelength LEDhaving the light emitting peak wavelength in a range of 360 nm to 420 nmis obtained with low cost, however includes only a range of the lightemitting wavelength limited by the long-wavelength. Accordingly, it isdifficult for the emitted ultraviolet light to reach the inner portionof the ink droplet which is landed on the recording medium, and only thesurface of the ink coating film is first cured. Thus, when curing theultraviolet curable ink (at least the first ultraviolet curable ink) inwhich transmittance at a wavelength of 395 nm is equal to or less than1%, the cured wrinkles tend to be easily generated (wrinkles tend to beeasily generated on the surface of the cured film). Here, the inventorsof the present application have found that it is possible to reduce thecured wrinkles even in a case of using the long-wavelength LED, bysetting the irradiation peak intensity to be equal to or more than 800mW/cm². Accordingly, by setting the irradiation peak intensity of thefirst ultraviolet curable ink to be relatively high, it is possible toperform both curing almost at the same time without delay of the curingof the inner portion of the ink coating film compared to the curing ofthe surface thereof, and to prevent the cured wrinkles. Thus, glossinessbecomes high and shiny appearance is excellent. In a case of using thefirst ultraviolet curable ink, and when the irradiation peak intensityis small, the reason of easy generation of the cured wrinkles isexpected as a significantly low curing speed for such ink in the innerportion of the coating film compared to a curing speed in the surface ofthe coating film. However, the reason is not limited thereto.

In addition, the ultraviolet curable ink containing the radicalphotopolymerization initiator and the radical polymerization compoundhas a high curing speed, and particularly it is possible to obtain ahigh curing speed, even with the ultraviolet irradiation from the lightsource including the limited light emitting peak wavelength as the LED.However, in a case of using the ink, the problem in that the curedwrinkles are easily generated occurs. The inventors of the presentapplication also found that a high-quality recorded material withexcellent hardenability and no cured wrinkles can be obtained by settingthe irradiation peak intensity to be equal to or more than 800 mW/cm²,even in a case of using such ink.

Herein, the ultraviolet irradiation with the irradiation peak intensityof equal to or more than 800 mW/cm² may be performed one time, or may beperformed two or more times. In addition, in a case of performing theultraviolet irradiation two or more times, the ultraviolet irradiationcan be performed plural times from the same light source, or theultraviolet irradiation may be performed one or more times from eachdifferent light source.

In addition, since the irradiation peak intensity can suppress the costof the irradiator and can prevent heat generation or light leakage fromthe light source from affecting the head to obtain excellent dischargingstability, the irradiation peak intensity is preferable to be 800 mW/cm²to 4000 mW/cm², more preferable to be 800 mW/cm² to 2000 mW/cm², andfurther preferable to be 1000 mW/cm² to 2000 mW/cm².

In addition, for the irradiation peak intensity of the presentspecification, a value which is measured using an ultraviolet meterUM-10 and a receptor UM-400 (all manufactured by KONICA MINOLTA SENSING,INC.) is used. However, the measuring method of the irradiation peakintensity is not limited, and a well-known measuring method of therelated art can be used.

In addition, the irradiation energy at the time of the irradiation ispreferable to be 100 mJ/cm² to 600 mJ/cm², more preferable to be 200mJ/cm² to 600 mJ/cm², and further preferable to be 200 mJ/cm² to 500mJ/cm². If the irradiation energy is in the range described above, anexcellent hardenability is obtained, and it is possible to suppress thecost of the irradiation units necessary for the irradiation.

In addition, the irradiation energy of the present specification iscalculated by multiplying the irradiation peak intensity by the timefrom the irradiation start to the irradiation end, and in a case of thepulse irradiation LED, the Duty ratio is further multiplied for thecalculation.

Herein, the ultraviolet irradiation with the irradiation peak intensityof equal to or more than 800 mW/cm² may be performed plural times. Inthis case, the irradiation energy is expressed as the irradiation energyamount obtained by adding the irradiation of the plural times. Inaddition, in a case of performing the irradiation with the irradiationpeak intensity of equal to or more than 800 mW/cm² plural times, forfurther excellent discharging stability, the irradiation energy in theirradiation initially performed after the discharging is preferable tobe equal to or less than 800 mJ/cm², more preferable to be equal to orless than 400 mJ/cm², further preferable to be equal to or less than 200mJ/cm², and further more preferable to be 50 mJ/cm² to 200 mJ/cm².

When the irradiation peak intensity, the irradiation energy, and thelight emitting peak wavelength described above are in the preferableranges, the curing is performed with a low energy and at a high speedwith the composition of the ink which will be described later. Inaddition, it is possible to shorten the irradiation time by thecomposition of the ink which will be described later, and in this case,the recording speed increases. Meanwhile, it is possible to reduce theirradiation peak intensity by the composition of the ink which will bedescribed later, and in this case, the miniaturization of the apparatusand reduction of the cost is realized.

In addition, as described above, in the curing step, it is preferable tofurther perform irradiation with ultraviolet light, after the firstultraviolet curable ink is initially irradiated with ultraviolet lightfrom the UV-LED having the irradiation peak intensity of equal to ormore than 800 mW/cm². The light source in a case of further irradiatingthe first ultraviolet curable ink with ultraviolet light is notparticularly limited as described above, and the irradiation peakintensity, the irradiation energy, and the peak wavelength are notparticularly limited, however in a case where the curing is notsufficiently performed with the first irradiation, that is, in a case ofpreliminary curing, it is preferable to have an irradiation energy toperform sufficient curing (proper curing). In addition, the number ofthe light sources or the number of times of the irradiation when furtherirradiating is not particularly limited.

In addition, for obtaining the same advantageous effects as describedabove, the light emitting peak wavelength when initially irradiates thefirst ultraviolet curable ink with ultraviolet light is preferable to bein a range of 360 nm to 420 nm, and more preferable to be in a range of380 nm to 410 nm.

Ink Jet Recording Method Using an Ink Set

An ink jet recording method in a case of using an ink set including thefirst ultraviolet curable ink will be further described from the ink jetrecording method described above.

From the ink jet recording method in a case of using the ink set, an inkjet recording method further including a discharging step of dischargingultraviolet curable ink (hereinafter, also referred to as “secondultraviolet curable ink”) of a radical polymerization reaction type inwhich a radical photopolymerization initiator and a radicalpolymerization compound is included and transmittance at a wavelength395 nm exceeds 1%, onto a recording medium, and a curing step of curingthe second ultraviolet curing ink which is landed on the recordingmedium by irradiating the ink with ultraviolet light, is preferable. Inaddition, it is more preferable that the light source which initiallyemits ultraviolet light in the curing step be an UV-LED having theirradiation peak intensity of less than 800 mW/cm². In this case, it ispossible to uneven brightness which can be generated between the coatingfilm of the first ultraviolet curable ink and the coating film of thesecond ultraviolet curable ink.

Herein, the irradiation peak intensity will be further described. Whencuring the ultraviolet curable ink such as the second ultravioletcurable ink in which transmittance at a wavelength of 395 nm exceeds 1%,if the light source having the irradiation peak intensity of equal to ormore than 800 mW/cm² is used in the same manner as the case of the firstultraviolet curable ink, the shiny appearance tends to become high.However, when performing multi-color printing using the firstultraviolet curable ink and the second ultraviolet curable ink, it isdifficult to balance shiny appearance with an image portion of the firstultraviolet curable ink due to extremely high shiny appearance of animage portion of the second ultraviolet curable ink. As a result, unevenbrightness is observed between each image portion. Here, the inventorsof the present application have found that, it is possible to preventgeneration of the cured wrinkles and to reduce the uneven brightness, bysetting the irradiation peak intensity of the second ultraviolet curableink to be relatively low to be less than 800 mW/cm², when performing themulti-color printing.

The irradiation peak intensity from the UV LED is more preferable to be100 mW/cm² to 700 mW/cm², and further preferable to be 100 mW/cm² to 500mW/cm². In addition, the irradiation energy when irradiating the secondultraviolet curable ink with ultraviolet light is preferable to be equalto or less than 500 mJ/cm², and more preferable to be 100 mJ/cm² to 400mJ/cm². If the irradiation peak intensity and the irradiation energy arein the range described above, the hardenability and dischargingstability also become excellent.

The discharging step and the curing step using the first ultravioletcurable ink and the discharging step and the curing step using thesecond ultraviolet curable ink may be performed in any order, and theorder is not particularly limited. After performing to the process ofthe curing of the first ultraviolet curable ink, the discharging step ofthe second ultraviolet curable ink may be performed, or after performingto the process of curing the second ultraviolet curable ink, thedischarging step of the first ultraviolet curable ink may be performed.In addition, each curing step is not limited to a curing step ofperforming sufficient curing, and may be a curing step of curing atleast a part of the ink, or the sufficient curing may not be performedfinally.

Among them, it is preferable to subsequently perform the dischargingstep and the curing step using the second ultraviolet curable ink, aftersequentially performing the discharging step and the curing step usingthe first ultraviolet curable ink. In this case, it is possible toreduce the irradiation energy in the curing step of the firstultraviolet curable ink.

Further, after performing each curing step of the first ultravioletcurable ink and the second ultraviolet curable ink, a curing step ofcuring the first ultraviolet curable ink and the second ultravioletcurable ink by further irradiating the ink with ultraviolet light, maybe provided. By providing the additional curing step described above, itis also possible to reduce the irradiation energy in the curing step ofthe second ultraviolet curable ink.

Further, in a case of performing multi-color printing with multicolorink by a plurality of heads using the recording apparatus shown in FIG.2, by performing minimum irradiation for preventing color mixing foreach head and finally collectively irradiating the multicolor ink withintensity of equal to or more than 800 mW/cm², it is possible tosuppress the cost of the light source to be extremely low.

In addition, for obtaining the same advantageous effects as describedabove, the light emitting peak wavelength when it initially irradiatesthe second ultraviolet curable ink with ultraviolet light is preferableto be in a range of 360 nm to 420 nm, and more preferable to be in arange of 380 nm to 410 nm.

Recording Medium

A recorded material is obtained by discharging the ink onto therecording medium by using the ink jet recording method of theembodiment. As the recording medium, for example, an ink absorbable ornon-absorbable recording medium is used. The ink jet recording method ofthe embodiment can be widely applied to recording media having variousabsorption properties, such as a non-absorbable recording medium inwhich permeation of water-soluble ink is difficult, and an absorbablerecording medium in which permeation of ink is easy.

As the absorbable recording medium, it is not particularly limited, andfor example, plain paper such as electrophotographic paper having highpermeability of ink, ink jet paper (exclusive paper for ink jetincluding an ink absorbing layer configured of silica particles oralumina particles, or an ink absorbing layer configured of hydrophilicpolymer such as polyvinyl alcohol (PVA) or polyvinylpyrrolidone (PVP)),art paper, coated paper, or cast paper which is used for general offsetprinting having relatively low permeability of water-based ink, or thelike, is used.

As the non-absorbable recording medium, it is not particularly limited,and for example, a plastic film or plate such as polyvinyl chloride,polyethylene, polypropylene, polyethylene terephthalate (PET), or thelike, a metallic plate such as iron, silver, copper, aluminum, or thelike, or metallic plate or plastic film obtained by manufacturing byvapor disposition of each metals thereof, alloy plate such as stainlessor brass, or the like is used.

As described above, according to the embodiment, it is possible toprovide an ink jet recording method which can have an excellenthardenability, effectively prevent cured wrinkles, and further haveexcellent abrasion resistance, discharging stability, and bleedresistance.

Among the effects realized by the embodiment described above,hardenability will be described in detail. In a case of a relativelythin film thickness of a cured film and a radical polymerizationreaction system, hardenability is degraded due to effect of oxygeninhibition. If sufficient irradiation is performed, an excellenthardenability can be secured, however, in a case of using a relativelythick cured film, a problem of degradation of the recording imagequality occurs due to generation of cured wrinkles. To this, accordingto the embodiment, it is possible to suppress generation of curedwrinkles.

Ultraviolet Curable Ink

An embodiment of the invention relates to ultraviolet curable ink. Theultraviolet curable ink is at least the first ultraviolet curable ink ofa radical polymerization reaction type, and is used in the ink jetrecording method of the embodiment described above. In addition, thefirst ultraviolet curable ink contains the radical photopolymerizationinitiator and the radical polymerization compound, and has transmittanceat a wavelength of 395 nm to be equal to or less than 1%.

Herein, the ultraviolet curable ink can be classified into radicalpolymerization reaction type ink and cation polymerization reaction typeink, from the difference in polymerization reaction mechanism thereof.Among them, the ultraviolet curable ink of cation polymerizationreaction type contains a cation photopolymerization initiator and acation polymerization compound, and, cured wrinkles are difficult to begenerated due to a low coefficient of polymerization volumetricshrinkage. Accordingly, it is substantially unnecessary to set theirradiation intensity of initial irradiation to be equal to or more than800 mW/cm², for the ultraviolet curable ink of cation polymerizationreaction type.

Meanwhile, among them, the ultraviolet curable ink of radicalpolymerization reaction type is ink containing the radicalphotopolymerization initiator and the radical polymerization compound,and is ink in that radical photopolymerization initiator generatesradical by the irradiation with ultraviolet light, and polymerizationreaction of the radical polymerization compound is promoted. Theultraviolet curable ink of radical polymerization reaction type isadvantageous in that an ink material is inexpensive, there are manytypes of radical polymerization compound, and it is easy to deal withvarious requirements such as film quality, however, a problem in thatthe cured wrinkles are easily generated occurs due to a high coefficientof polymerization volumetric shrinkage.

Here, it is possible to effectively prevent generation of cured wrinklesby using the predetermined ultraviolet curable ink of the radicalpolymerization reaction type in the ink jet recording method of theembodiment described above. Accordingly, the significant effects areobtained when using the ultraviolet curable ink of the radicalpolymerization reaction type than the cation polymerization reactiontype, in the ink jet recording method described above.

Hereinafter, an additive (component) which is contained or may becontained at least in the first ultraviolet curable ink among theultraviolet curable ink of the embodiment (hereinafter, simply referredto as “ink”), will be described.

In the ultraviolet curable ink other than the first ultraviolet curableink, not otherwise specified, the following components may be or may notbe contained, and other well-known components of the related art may becontained. As the ultraviolet curable ink other than the firstultraviolet curable ink, the second ultraviolet curable ink and inkother than the second ultraviolet curable ink which will be describedlater are used.

Radical Polymerization Compound

The radical polymerization compound included in the ink is polymerizedat the time of light irradiation with the operation of the radicalphotopolymerization which will be described later and the printed inkcan be cured.

The radical polymerization compound included in the ink is polymerizedat the time of light irradiation with the operation of the radicalphotopolymerization which will be described later and it is possible tocure printed ink. As the radical polymerization compound, variousmonofunctional, bifunctional, and trifunctional or more ofpolyfunctional monomers and oligomers which are well known in therelated art can be used. As the monomer, unsaturated carboxylic acidsuch as (meth)acrylate, itaconate, crotonate, isocrotonic acid, andmaleic acid, or salt thereof, ester, urethane, amide, and anhydridethereof, acrylonitrile, styrene, various unsaturated polyester,unsaturated polyether, polyether polyamides, and unsaturated urethane,are used for example. In addition, as the oligomers, an oligomer formedfrom the monomers described above such as a straight-chain acrylicoligomer or the like, epoxy (meth)acrylate, oxetane (meth)acrylate,aliphatic urethane (meth)acrylate, aromatic urethane (meth)acrylate, andpolyester (meth)acrylate are used for example.

In addition, as the other monofunctional monomer or multifunctionalmonomer, an N-vinyl compound may be contained. As the N-vinyl compound,N-vinyl formamide, N-vinyl carbazole, N-vinyl acetamide, N-vinylpyrrolidone, N-vinyl caprolactam, and acryloylmorpholine, andderivatives thereof are used, for example.

Among the radical polymerization compounds, ester of (meth)acrylate,that is, (meth)acrylate is preferable.

Among the (meth)acrylate, as monofunctional (meth)acrylate,monofunctional (meth)acrylate having an aromatic ring skeleton such asisoamyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate,octyl (meth)acrylate, decyl (meth)acrylate, isomyristyl (meth)acrylate,isostearyl (meth)acrylate, 2-ethylhexyl-diglycol (meth)acrylate,2-hydroxy butyl (meth)acrylate, butoxyethyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxy diethylene glycol(meth)acrylate, methoxy polyethylene glycol (meth)acrylate, methoxypropylene glycol (meth)acrylate, tetrahydro furfuryl (meth)acrylate,isobornyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl(meth)acrylate, lactone-modified flexible (meth)acrylate, t-butylcyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate,dicyclopentenyloxyethyl (meth)acrylate, phenoxyethyl (meth)acrylate,phenoxy diethylene glycol (meth)acrylate, 2-hydroxy-3-phenoxypropyl(meth)acrylate, and benzyl (meth)acrylate, and vinyl ethergroup-containing (meth)acrylate esters expressed by the followingGeneral Formula (I), are used, for example.

CH₂═CR¹—COOR²—O—CH═CH—R³  (I)

In Formula (I), R¹ represents a hydrogen atom or a methyl group, R²represents a divalent organic residue having 2 to 20 carbon atoms, andR³ represents a hydrogen atom or a monovalent organic residue having 1to 11 carbon atoms.

Among them, since it is possible to obtain an excellent hardenabilityand have low viscosity of the ink, at least any of vinyl ethergroup-containing (meth)acrylate esters represented by the GeneralFormula (I) and phenoxyethyl (meth)acrylate expressed is preferable.

Among (meth)acrylate described above, as bifunctional (meth)acrylate,diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate,tetraethylene glycol di(meth)acrylate, polyethylene glycoldi(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropyleneglycol di(meth)acrylate, polypropylene glycol di(meth)acrylate,1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate,1,9-nonanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate,dimethylol-tricyclodecane di(meth)acrylate, bisphenol A EO (ethyleneoxide) adduct di(meth)acrylate, bisphenol A PO (propylene oxide) adductdi(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate,and polytetramethyleneglycol di(meth)acrylate are used, for example.Among them, at least any of diethylene glycol di(meth)acrylate andtripropylene glycol di(meth)acrylate is preferable.

Among (meth)acrylate described above, as trifunctional or more ofpolyfunctional (meth)acrylate, trimethylolpropane tri(meth)acrylate,EO-modified trimethylolpropane tri(meth)acrylate, pentaerythritoltri(meth)acrylate, pentaerythritol tetra(meth)acrylate,dipentaerythritol hexa(meth)acrylate, ditrimethylol propanetetra(meth)acrylate, glycerine propoxy tri(meth)acrylate,caprolactone-modified trimethylolpropane tri(meth)acrylate,pentaerythritol tetra(meth)acrylate, and caprolactam-modifieddipentaerythritol hexa(meth)acrylate are used, for example.

Vinyl ether group-containing (meth)acrylate esters expressed by GeneralFormula (I) will be described in detail. In General Formula (I), as thedivalent organic residue having 2 to 20 carbon atoms represented by R²,a straight, branched, or cyclic alkylene group having 2 to 20 carbonatoms which may be substituted, an alkylene group including oxygen atomsdue to ether bond and/or ester bond in a structure and having 2 to 20carbon atoms which may be substituted, and a divalent aromatic grouphaving 6 to 11 carbon atoms which may be substituted are preferable.Among them, an alkylene group having 2 to 6 carbon atoms such as anethylene group, an n-propylene group, an isopropylene group, and abutylene group, and an alkylene group having oxygen atoms due to etherbond in a structure and having 2 to 9 carbon atoms such as anoxyethylene group, an oxy n-propylene group, an oxy isopropylene group,an oxybutylene group are preferably used.

In General Formula (I), as the monovalent organic residue having 1 to 11carbon atoms represented by R³, a straight, branched, or cyclic alkylgroup having 1 to 10 carbon atoms which may be substituted, and anaromatic group having 6 to 11 carbon atoms which may be substituted arepreferable. Among them, an alkyl group having 1 or 2 carbon atoms suchas a methyl group or an ethyl group, and an aromatic group having 6 to 8carbon atoms such as a phenyl group and a benzene group are preferablyused.

In a case where each organic residue is a group which may besubstituted, the substituent thereof is divided into a group containingcarbon atoms and a group not containing carbon atoms. First, in a casewhere the substituent is a group containing carbon atoms, the number ofthe carbon atoms are counted as the number of carbon atoms in theorganic residue. The group containing carbon atoms is not limited to thefollowing, however, a carboxyl group and an alkoxy group are used, forexample. Next, the group not containing carbon atoms are not limited othe following, however, a hydroxyl group and a halo group are used, forexample.

Among vinyl ether group-containing (meth)acrylate esters, since thelower viscosity of the ink, a high flash point, and an excellenthardenability of ink can be obtained, 2-(vinyloxyetoxy) ethyl(meth)acrylate, that is, at least any of 2-(vinyloxyetoxy) ethylacrylate and 2-(vinyloxyetoxy) ethyl methacrylate is preferable, and2-(vinyloxyetoxy) ethyl acrylate is more preferable. Particularly, sinceall of 2-(vinyloxyetoxy) ethyl acrylate and 2-(vinyloxyetoxy) ethylmethacrylate have simple structure and small molecular weight, it ispossible to significantly lower viscosity of ink. As 2-(vinyloxyetoxy)ethyl (meth)acrylate, 2-(2-vinyloxyetoxy) ethyl (meth)acrylate and2-(1-vinyloxyetoxy) ethyl (meth)acrylate are used, and as2-(vinyloxyetoxy) ethyl acrylate, 2-(2-vinyloxyetoxy) ethyl acrylate and2-(1-vinyloxyetoxy) ethyl acrylate are used. In addition,2-(vinyloxyetoxy) ethyl acrylate is more excellent in viewpoint ofhardenability, compared to 2-(vinyloxyetoxy) ethyl methacrylate.

Vinyl ether group-containing (meth)acrylate esters described above maybe used alone, or may be used in combination of two or more kinds.

As a manufacturing method of vinyl ether group-containing (meth)acrylateesters described above, it is not limited to the following, however, amethod of esterifying (meth)acrylate and hydroxyl group-containing vinylether (manufacturing method B), a method of esterifying halide(meth)acrylate and hydroxyl group-containing vinyl ether (manufacturingmethod C), a method of esterifying (meth)acrylic anhydride and hydroxylgroup-containing vinyl ether (manufacturing method D), a method ofesterifying (meth)acrylic ester and hydroxyl group-containing vinylether (manufacturing method E), a method of esterifying (meth)acrylateand halogen-containing vinyl ether (manufacturing method F), a method ofesterifying (meth)acrylate alkali (earth) metal salt andhalogen-containing vinyl ether (manufacturing method G), a method oftransvinylation of hydroxyl group-containing (meth)acrylic ester andvinyl carboxylic acid (manufacturing method H), a method oftransetherification of hydroxyl group-containing (meth)acrylic ester andalkyl vinyl ether (manufacturing method I) are used. Among them, themanufacturing method E is preferable since it is possible to excellentlyexhibit desirable effects of the embodiment.

Among the radical polymerization compound described above, since the inkof the embodiment is further excellent to realize low viscosity,hardenability, and solubility of the radical photopolymerizationinitiator, it is preferable to contain at least any of monofunctional(meth)acrylate and bifunctional or more (meth)acrylate, and it is morepreferable to contain both thereof. In this case, low viscosity of inkis obtained, excellent solubility of the radical photopolymerizationinitiator and the other additive is obtained, excellent dischargingstability at the time of ink jet recording is easily obtained, andfurther high toughness, heat resistance, and chemical resistance of thecoating film are increased.

The radical polymerization compound described above may be used along,or may be used in combination of two or more types.

Content of the radical polymerization compound described above ispreferable to be equal to or less than 95% by mass, with respect to thetotal mass (100% by mass) of the ink. Particularly, the total content ofmonofunctional (meth)acrylate is preferable to be 30% by mass to 90% bymass and more preferable to be 40% by mass to 80% by mass, with respectto the total mass (100% by mass) of the ink. Herein, in a case ofcontaining monofunctional (meth)acrylate which is vinyl ethergroup-containing (meth)acrylate ester described above, the total contentdescribed above means content including vinyl ether group-containing(meth)acrylate ester described above.

In addition, among the monofunctional (meth)acrylate, in a case ofcontaining monofunctional (meth)acrylate other than vinyl ethergroup-containing (meth)acrylate ester described above, the contentthereof is preferable to be 20% by mass to 80% by mass, and morepreferable to be 30% by mass to 70% by mass, with respect to the totalcontent (100% by mass) of the ink.

Further, in a case of vinyl ether group-containing (meth)acrylate esterdescribed above contained in the ink as monofunctional (meth)acrylate,the content of vinyl ether group-containing (meth)acrylate esterdescribed above is preferable to be 10% by mass to 70% by mass, and morepreferable to be 10% by mass to 50% by mass, with respect to the totalcontent (100% by mass) of the ink.

By setting the content in the range described above, it is possible torealize further excellent hardenability of the ink, hardenability due tosolubility of the radical photopolymerization initiator, viscosityreduction, and preservation stability. In particular, by containingmonofunctional (meth)acrylate including an aromatic skeleton in the inkamong monofunctional (meth)acrylate, further excellent hardenability,viscosity reduction, and solubility of the radical photopolymerizationinitiator are obtained. In addition, in a case of containingbifunctional or more (meth)acrylate, the content thereof is preferableto be 5% by mass to 60% by mass, more preferable to be 10% by mass to50% by mass, and further preferable to be 10% by mass to 40% by mass,with respect to the total content (100% by mass) of the ink, since it ispossible to obtain further excellent hardenability, abrasion resistance,and adhesiveness.

Radical Photopolymerization Initiator

The ink of the embodiment contains the radical photopolymerizationinitiator. The radical photopolymerization initiator is used forperforming printing by curing the ink existing on a surface of arecording medium with radical polymerization by the irradiation withultraviolet light. By using ultraviolet light (UV), it is possible toobtained excellent safety and to suppress cost of a light source lamp.By the energy of the light (ultraviolet light), radical active speciesare generated and polymerization of the radical polymerization compoundis initiated.

As the radical photopolymerization initiator, aromatic ketones, acylphosphine oxide compounds, aromatic onium salt compounds, organicperoxides, thio compounds (such as thioxanthone compounds, thiophenylgroup-containing compounds), α-aminoalkylphenone compounds,hexaarylbiimidazole compounds, ketoxime ester compounds, boratecompounds, azinium compounds, metallocene compounds, active estercompounds, compounds having carbon-halogen bond, and alkylaminecompounds are used, for example.

Among them, since it is possible to realize further excellenthardenability of the ink, acyl phosphine oxide compounds are preferable.

As detailed examples of the radical photopolymerization initiator,acetophenone, acetophenone benzyl ketal, 1-hydroxy cyclohexyl phenylketone, 2,2-dimethoxy-2-phenylacetophenone, xanthone, fluorenone,benzaldehyde, fluorene, anthraquinone, triphenylamine, carbazole,3-methylacetoacetate phenone, 4-chloro benzophenone,4,4′-dimethoxy-benzophenone, 4,4′-diamino benzophenone, Michler'sketone, benzoin propyl ether, benzoin ethyl ether, benzyl dimethylketal, 1-(4-isopropyl-phenyl)-2-hydroxy-2-methyl-propan-1-one,2-hydroxy-2-methyl-1-phenyl propan-1-one, thioxanthone, diethylthioxanthone, 2-isopropylthio xanthone, 2-chlorothioxanthone,2-methyl-1-[4-(methylthio) phenyl]-2-morpholino-propan-1-one, bis(2,4,6-trimethyl benzoyl)-phenyl phosphine oxide, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, 2,4-diethyl thioxanthone, andbis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxide areused.

As commercially available products of the radical photopolymerizationinitiator, IRGACURE 651 (2,2-dimethoxy-1,2-diphenyl ethane-1-one),IRGACURE 184 (1-hydroxy-cyclohexyl-phenyl-ketone), DAROCUR 1173(2-hydroxy-2-methyl-1-phenyl-propan-1-one), IRGACURE 2959(1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one),IRGACURE 127 (2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]phenyl}-2-methyl-propane-1-one), IRGACURE 907(2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one), IRGACURE 369(2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1), IRGACURE379 (2-(dimethylamino)-2-[(4-methylphenyl) methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone), DAROCUR TPO(2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide), IRGACURE 819 (bis(2,4,6-trimethyl benzoyl)-phenyl phosphine oxide), IRGACURE 784 (bis(η5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)-phenyl) titanium), IRGACURE OXE 01(1,2-octane dione, 1-[4-(phenylthio)-, 2-(O-benzoyloxime)]), IRGACUREOXE 02 (ethanone, 1-[9-ethyl-6-(2-methyl-benzoyl)-9H-carbazol-3-yl]-,1-(O-acetyl oxime)), IRGACURE 754 (mixture of oxyphenyl acetic acid,2-[2-oxo-2-phenylacetoxy ethoxy] ethyl ester and oxyphenyl acetic acid,and 2-(2-hydroxyethoxy) ethyl ester) (all manufactured by BASF),Speedcure TPO, Speedcure DETX (2,4-diethyl thioxanthone), Speedcure ITX(2-isopropylthioxanthone) (all manufactured by Lambson), KAYACURE DETX-S(2,4-diethyl thioxanthone) (manufactured by Nippon Kayaku Co., Ltd.),Lucirin TPO, LR8893, LR8970 (all manufactured by BASF), and UBECRYL P36(manufactured by UCB) are used, for example.

The radical photopolymerization initiator may be used along or may beused in combination of two or more kinds.

The content of the radical photopolymerization initiator is preferableto be 5% by mass to 15% by mass and more preferable to be 7% by mass to13% by mass, with respect to the total content (100% by mass) of theink. If the content thereof is in the range described above, it ispossible to sufficiently exhibit the ultraviolet curing speed, and toavoid residue of dissolved radical photopolymerization initiator orcoloring due to the initiator. It is preferable to contain acylphosphine oxide compounds among the radical photopolymerizationinitiator. The content of acyl phosphine oxide compounds described aboveis preferable to be 5% by mass to 15% by mass and more preferable to be7% by mass to 13% by mass, with respect to the total content (100% bymass) of the ink.

Color Material

The ink of the embodiment may further contain color materials.

As described above, in at least the first ultraviolet curable ink amongthe ink of the embodiment, transmittance at a wavelength of 395 nm isequal to or less than 1%. As the ink in which transmittance at awavelength of 395 nm is equal to or less than 1%, ink containing one ormore selected from a group consisting of a yellow color material, ablack color material, an orange color material, and a green colormaterial, is used. Since these color materials easily absorb light(ultraviolet light) having a wavelength of 395 nm, a problem in thatmost of ultraviolet emitted from an LED including a peak wavelength ataround 395 nm is not contributed to photopolymerization reaction. Here,in the embodiment, by setting the irradiation peak intensity to be greatto be equal to or more than 800 mW/cm², even when using the inkcontaining the color materials which easily absorb light (ultravioletlight) having a wavelength of 395 nm, the emitted ultraviolet light canbe sufficiently contributed to photopolymerization reaction.

On the other hand, among the ink of the embodiment, as ink in whichtransmittance at a wavelength of 395 nm exceeds 1%, ink containing atleast any of a cyan color material, a magenta color material, and awhite color material, or clear ink not containing color materials areused. In a case of irradiating the ink containing the color materialswith ultraviolet light from the LED, by setting the irradiation peakintensity to be relatively low to be less than 800 mW/cm², it ispossible to extremely suppress generation of difference in shinyappearance with the ink in which transmittance at a wavelength of 395 nmis equal to or less than 1%, and to effectively prevent unevenbrightness. In addition, since the transmittance at a wavelength of 395nm is slightly different depending to kinds of colors shown by the colormaterials and kinds of the color materials, and is different dependingon the content of the color materials in the ink, the transmittance isobtained by measuring for each ink. Among them, since the transmittanceis satisfied and the recording of a color image can be performed, as thefirst ultraviolet curable ink, the ink containing one or more selectedfrom a group consisting of a yellow color material, a black colormaterial, an orange color material, and a green color material ispreferable. In addition, since the transmittance is satisfied, therecording of a color image can be performed, and an excellent appearanceof a recorded material is obtained, the ink containing one or moreselected from a group consisting of a cyan color material, a magentacolor material, and a white color material, or the clear ink is morepreferable.

As the color material, at least one of a pigment and a dye can be used.Among, since excellent light resistance is obtained, the pigment ispreferable.

Pigment

By using the pigment as the color material, it is possible to obtainexcellent light resistance of the ink. Both an inorganic pigment and anorganic pigment can be used for the pigment.

As the inorganic pigment, carbon blacks (C.I. Pigment Black 7) such asfurnace black, lamp black, acetylene black, and channel black, ironoxide, titanium oxide can be used.

As the organic pigment, azo pigments such as insoluble azo pigments,condensed azo pigments, azo lake, and chelate azo, polycyclic pigmentssuch as phthalocyanine pigments, perylene and perinone pigments,anthraquinone pigments, quinacridone pigments, dioxane pigments,thioindigo pigments, isoindolinone pigments, and quinophthalonepigments, dye chelate (for example, basic dye chelate, acidic dyechelate, or the like), dye lake (basic dye lake, acidic dye lake, or thelike), nitro pigments, nitroso pigments, aniline black, and daylightfluorescent pigments are used.

In more detail, as carbon black used for the black ink, No. 2300, No.900, MCF88, No. 33, No. 40, No. 45, No. 52, MA7, MA8, MA100, No. 2200Band the like (all manufactured by Mitsubishi Chemical Corporation),Raven 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255, Raven 700and the like (all manufactured by Carbon Columbia), Regal 400R, Regal330R, Regal 660R, Mogul L, Monarch 700, Monarch 800, Monarch 880,Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400, andthe like (all manufactured by CABOT JAPAN K.K.), Color Black FW1, ColorBlack FW2, Color Black FW2V, Color Black FW18, Color Black FW200, ColorBlack S150, Color Black S160, Color Black 5170, Printex 35, Printex U,Printex V, Printex 140U, Special Black 6, Special Black 5, Special Black4A, Special Black 4 (all manufactured by Degussa), and Microlith Black0066 K (former Microlith Black C-K, manufactured by BASF) are used.

As the pigment used for the white ink, C.I. Pigment White 6, 18, and 21are used.

As the pigment used for the yellow ink, C.I. Pigment Yellow 1, 2, 3, 4,5, 6, 7, 10, 11, 12, 13, 14, 16, 17, 24, 34, 35, 37, 53, 55, 65, 73, 74,75, 81, 83, 93, 94, 95, 97, 98, 99, 108, 109, 110, 113, 114, 117, 120,124, 128, 129, 133, 138, 139, 147, 151, 153, 154, 155, 167, 172, and 180are used.

As the pigment used for the magenta ink, C.I. Pigment Red 1, 2, 3, 4, 5,6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30, 31, 32,37, 38, 40, 41, 42, 48(Ca), 48(Mn), 57(Ca), 57:1, 88, 112, 114, 122,123, 144, 146, 149, 150, 166, 168, 170, 171, 175, 176, 177, 178, 179,184, 185, 187, 202, 209, 219, 224, and 245, or C.I. Pigment Violet 19,23, 32, 33, 36, 38, 43, and 50 are used.

As the pigment used for the cyan ink, C.I. Pigment Blue 1, 2, 3, 15,15:1, 15:2, 15:3, 15:34, 15:4, 16, 18, 22, 25, 60, 65, and 66, and C.I.Vat Blue 4 and 60 are used.

In addition, as the pigment other than magenta, cyan, and yellow, C.I.Pigment Green 7 and 10, C.I. Pigment Brown 3, 5, 25, and 26, C.I.Pigment Orange 1, 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, and63 are used.

The pigment may be used alone, or may be used in combination of two ormore kinds.

In a case of using the pigment described above, an average particle sizethereof is preferable to be equal to or less than 300 nm and morepreferable to be 50 nm to 200 nm. If the average particle size thereofis in the range described above, it is possible to obtain furtherexcellent reliability such as discharging stability or dispersionstability of the ink, and to form an image with excellent image quality.Herein, the average particle size of the embodiment is measured with adynamic light scattering method.

Dye

A dye can be used as the color material. As the dye, it is notparticularly limited, and an acidic dye, a direct dye, a reactive dye,and a basic dye can be used. As the dye, C.I. Acid Yellow 17, 23, 42,44, 79, and 142, C.I. Acid Red 52, 80, 82, 249, 254, and 289, C.I. AcidBlue 9, 45, and 249, C.I. Acid Black 1, 2, 24, and 94, C.I. Food Black 1and 2, C.I. Direct Yellow, 1, 12, 24, 33, 50, 55, 58, 86, 132, 142, 144,and 173, C.I. Direct Red 1, 4, 9, 80, 81, 225, and 227, C.I. Direct Blue1, 2, 15, 71, 86, 87, 98, 165, 199, and 202, C.I. Direct Black 19, 38,51, 71, 154, 168, 171, and 195, C.I. Reactive Red 14, 32, 55, 79, and249, C.I. Reactive Black 3, 4, and 35 are used, for example.

The dye described above may be used alone, or may be used in combinationof two or more kinds.

Since excellent shielding property and color reproducibility areobtained, the content of the color material is preferable to be 0.2% bymass to 10% by mass and more preferable to be 0.5% by mass to 8% bymass, with respect to the total content (100% by mass) of the ink.

Dispersant

When the ink contains the pigment, the ink may further contain adispersant for obtaining further excellent pigment dispersibility. Asthe dispersant, it is not particularly limited, and a dispersant whichis commonly used for preparing a pigment dispersion liquid such as apolymer dispersant, is used. As detailed examples, a dispersantincluding one or more of polyoxyalkylene polyalkylene polyamine, vinylpolymer and copolymer, acrylic polymer and copolymer, polyester,polyamide, polyimide, polyurethane, amino-based polymer,silicon-containing polymer, sulfur-containing polymer,fluorine-containing polymer, and epoxy resin, as main components, areused. As commercially available products of the polymer dispersant,Ajisper Series manufactured by Ajinomoto Fine-Techno Co., Inc.,Solsperse Series (such as Solsperse 36000) which can be purchased fromAvecia or Noveon, DISPERBYK Series manufactured by BYK Chemie, andDISPARLON Series manufactured by Kusumoto Chemicals, Ltd. are used.

Slip Agent

The ink of the embodiment may further contain a slip agent (surfactant).As the slip agent, it is not particularly limited, and as silicone basedsurfactant, polyester-modified silicone or polyether-modified siliconecan be used, for example, and it is particularly preferable to usepolyester-modified polydimethylsiloxane or a polyether modifiedpolydimethylsiloxane. As detailed example, BYK-347, BYK-348, BYK-UV3500,3510, 3530, and 3570 (all manufactured by BYK) can be used.

The slip agent may be used alone and may be used in combination of twoor more kinds. In addition, the content of the slip agent is notlimited, and a preferable amount may be suitably added.

Other Additives

The ink may further contain additives (components) other than theadditives described above. As such component, it is not particularlylimited, and a polymerization accelerator, a polymerization inhibitor, apermeation accelerator, and a wetting agent (moisturizing agent) whichare well known in the related art may be used, for example. As the otheradditives, a fixing agent, an antifungal agent, a preservative, anantioxidant, an ultraviolet absorbing agent, a chelate, pH adjuster, anda thickener which are well known in the related art may be used, forexample.

Hereinafter, an embodiment of a second invention will be described indetail. The invention is not limited to the following embodiment, andvarious modifications can be performed in a range not departing from thegist of the invention. In addition, in each drawing used in thefollowing description, scale of each constituent element (member) isappropriately changed for a size of each constituent element to bevisually recognized on the drawings. The embodiments are not onlylimited to a ratio of quantity, a shape and a size of the constituentelements and a relative positional relationship of each constituentelement described in the drawings.

In the present specification, a “hardenability” refers to a property forcuring by photoresponse. “Cured wrinkles” mean wrinkles which aregenerated on a surface of a coating film after curing, as describedabove. “Abrasion resistance” refers to a property in which it isdifficult for a cured material to be peeled off and to be scratched whenthe cured material is rubbed. “Discharging stability” refers to aproperty which is to be able to discharge ink droplets which are alwaysstable without clogging of a nozzle, from a nozzle. “Bleed” meansbleeding and “bleed resistance” refers to a property in which bleedinghardly occurs on the edge of an image. “Preservation stability” refersto a property wherein the viscosity before and after storage is hardlychanged when an ink is stored.

In this specification, “(meth)acrylate” means at least any of acrylateand methacrylate corresponding thereto, “(meth)acryl” means at least anyof acryl and methacryl corresponding thereto, and “(meth)acryloyl” meansat least any of acryloyl and methacryloyl corresponding thereto.

Ink Jet Recording Apparatus

A first embodiment of the invention relates to an ink jet recordingapparatus, that is, a printer. The recording apparatus is used with anink jet recording method which will be described later. FIG. 2 is aschematic view of a recording area circumference in one aspect of a lineprinter.

As types of the printer in the embodiment, a line printer and a serialprinter are used, and these printers are used with different printersystem. To described briefly, a line printer includes a line head havinga length equal to or greater than a length corresponding to a width of arecording medium, and preferably having a length (width of recordingmedium) corresponding to a width of a recording medium, and the head is(substantially) not moved, and is fixed, and the recording is performedwith one pass (single pass). On the other hand, a serial printernormally performs recording by two or more passes (multi passes) whilereciprocating (shuttle movement) of a head in a direction orthogonal toa transportation direction of a recording medium. In the embodiment, anysystem printers can be used.

Among them, as will be described later, a line printer (line ink jetrecording apparatus) is a printer which forms an image only by singlescanning of a recording medium in a predetermined direction(hereinafter, referred to as “transportation direction”). Accordingly, aline printer is preferable from a viewpoint of a significantly highprinting rate, compared to a serial printer, however, problems in thatan ink discharge amount per one pass is large and cured wrinkles areeasily generated, occur. Here, significant effects of the embodimentcapable of preventing generation of cured wrinkles are particularlyexhibited with respect to a line printer. Hereinafter, a line printerwill be described with reference to FIG. 1 and FIG. 2.

A printer 1 is a recording apparatus which forms an image on a recordingmedium, and is communicatively connected to a computer 110 which is anexternal apparatus.

A printer driver is installed in the computer 110. The printer driver isa program for displaying a user interface to a display device (notshown) to convert image data output from an application program intorecording data (image forming data). The printer driver is recorded in a“computer-readable recording medium” such as a flexible disk (FD) or aCD-ROM. Alternatively, the printer driver can be downloaded to thecomputer 110 through Internet. In addition, the program is configuredfrom a code for realizing various functions.

In order to form an image by the printer 1, the computer 110 outputsrecording data corresponding to the image to the printer 1.

Here, the “recording apparatus” of the present specification means anapparatus which forms an image on a recording medium, and for example,corresponds to the printer 1. In addition, a “recording controllingapparatus” means an apparatus which controls a recording apparatus, andfor example, corresponds to the computer 110 in which the printer driveris installed.

The printer 1 of the embodiment is an apparatus which forms an image ona recording medium by discharging predetermined ultraviolet curable inkwhich is cured by irradiation with ultraviolet light. The predeterminedultraviolet curable ink contains at least vinyl ether group-containing(meth)acrylate esters and is cured by polymerization reaction due toirradiation with ultraviolet light.

A detailed ink composition of the ultraviolet curable ink will bedescribed later.

The printer 1 of the embodiment includes a transportation unit 20, ahead unit 30, an irradiation unit 40, a detector group 50, and acontroller 60. The printer 1 which received printing data from thecomputer 110 which is an external apparatus controls each unit, that is,the transportation unit 20, the head unit 30, and the irradiation unit40, by the controller 60, and forms an image on a recording medium Saccording to printing data. The controller 60 controls each unit andforms an image on the recording medium S, based on printing datareceived from the computer 110. The state in the printer 1 is monitoredby the detector group 50, and the detector group 50 outputs a detectionresult to the controller 60. The controller 60 controls each unit, basedon the detection result output from the detector group 50.

The transportation unit 20 is a unit which transports the recordingmedium S in a transportation direction. As shown in FIG. 2, thetransportation unit 20 includes an upstream transportation roller 23A, adownstream transportation roller 23B, and a belt 24, for example. Whenrotating the transportation roller (not shown), the upstreamtransportation roller 23A and the downstream transportation roller 23Bare rotated, and the belt 24 is rotated. The recording medium S which isfed by a paper feeding roller (not shown) is transported to a recordablearea (area opposing to the head), by the belt 24. By transporting therecording medium S by the belt 24, the recording medium S is moved withrespect to the head unit 30 in the transportation direction. Therecording medium S which passes the recordable area is discharged tooutside by the belt 24.

In addition, the recording medium S which is being transported iselectrostatic-adsorbed or vacuum-adsorbed to the belt 24. Herein, aphrase of “paper feeding” is used for convenience sake, however, as therecording medium of the embodiment, recording media which will bedescribed later can be used.

The head unit 30 is for discharging the ultraviolet curable ink to therecording medium S. By discharging each ink with respect to therecording medium S which is being transported, the head unit 30 formsdots on the recording medium S and forms an image. The printer 1 of theembodiment is a line printer, and each head of the head unit 30 can formdots corresponding to the width of the recording medium at one time. Indetail, as shown in FIG. 2 which is a schematic view of the recordingarea periphery of an aspect of the line printer in FIG. 1, in a casewhere each head of a white ink head W, a black ink head K, a cyan inkhead C, a magenta ink head M, and a yellow ink head Y is provided inorder from upstream of the transportation direction, a plurality ofheads are disposed so that each head can discharge dots corresponding tothe width of the recording medium S in a front direction from the backof a paper surface. As described above, by controlling each head fromthe upstream and forming dots in a necessary location in one linecorresponding to the width of the recording medium S, it is possible toform an image with only single scanning of the recording medium S in atransportation direction.

In addition, the white ink head W is a discharge unit of ultravioletcurable white ink. The black ink head K is a discharge unit ofultraviolet curable black ink. The cyan ink head C is a discharge unitof ultraviolet curable cyan ink. The magenta ink head M is a dischargeunit of ultraviolet curable magenta ink. The yellow ink head Y is adischarge unit of ultraviolet curable yellow ink.

The irradiation unit 40 irradiates the dots of ultraviolet curable inkwhich is landed on the recording medium S with ultraviolet light. Thedots formed on the recording medium S are cured by receiving emission ofthe ultraviolet light from the irradiation unit 40. As shown in FIG. 2,the irradiation unit 40 of the embodiment may include first irradiationunits 42 a to 42 e and a second irradiation unit 44.

The first irradiation unit 42 a to 42 e are for irradiating withultraviolet light for preliminarily curing the dots formed on therecording medium, and are positioned before the second irradiation unit44 which performs curing, that is, upstream of the transportationdirection. The “preliminary curing” herein is also called pinning, meanstemporary tacking, and in more detail, means curing for preventingbleeding between dots and controlling dot size. Accordingly, at leastonly a part of dots (liquid droplets), for example, a dot surface may becured.

Hereinafter, for differentiating with the preliminary curing, curingwhich is finally performed, that is, curing by emitting ultravioletlight from an ultraviolet light emitting diode (UV-LED) havingirradiation peak intensity of equal to or more than 800 mW/cm², isreferred to as “proper curing”.

The first irradiation units 42 a to 42 e are provided on downstream ofthe transportation directions of the white ink head W, the black inkhead K, the cyan ink head C, the magenta ink head M, and the yellow inkhead Y, respectively. That is, the first irradiation units are providedfor each ink color.

The first irradiation units 42 a to 42 e include ultraviolet lightemitting diodes (UV-LEDs) as light sources of ultraviolet irradiation.By controlling an amount of input current by the UV-LEDs, it is possibleto easily change an irradiation energy. The UV-LED is a type including acondensing lens (hereinafter, also referred to as a “lens-attachedLED”), and by irradiating by condensing light to a limited irradiationarea from the lens-attached LED, it is possible to maintain anirradiation energy and to perform spot irradiation with greaterirradiation peak intensity.

Hereinafter, the lens-attached LED will be described. FIG. 3 is across-sectional view schematically showing a part of an example of thelens-attached UV-LED, from the first irradiation unit.

An UV-LED 72 is mainly configured by an UV-LED chip 72 a and acondensing lens 72 b which emits ultraviolet light, and ultravioletlight which is issued by the UV-LED chip 72 a is condensed by thecondensing lens 72 b to form a given irradiation angle and emitted to alower portion of the first irradiation unit. The condensing lens 72 b isa package which covers the UV-LED chip 72 a, is formed of a lens formedon the surface thereof in a hemispherical shape and a cover protectingthe surface thereof, and condenses ultraviolet light issued from theUV-LED chip 72 a towards a center line of a hemisphere. A material ofthe lens or the cover is not limited as follows, however, for example,transparent resin such as glass, silicon resin, silicon rubber, and thelike can be used. The structure of the lens is not limited to the abovedescribed structure as long as the light condensing can be performed,and for example, may be a structure an attached lens which is separatelyformed in a hemispherical shape, other than a lens which is formed in ahemispherical shape integrally with the package. The UV-LED chip 72 aincluded in the irradiation unit 40 controls a supply current value byan UV-LED driving circuit (not shown) controlled by the controller 60,can rapidly switch an on state and an off state, and can emitultraviolet light having irradiation intensity necessary for curing theuncured ultraviolet curable ink which is landed on the recording mediumS. In addition, UV-LEDs are arranged in a line in the width directionand the transportation direction of the recording medium S, andconfigure each first irradiation unit. The positioning of the UV-LEDsarranged in a line in the transportation direction of the recordingmedium S in directions of the UV-LEDs arranged in a line in the widthdirection of the recording medium S, in a viewpoint of even distributionof irradiation areas where the light condensed from the UV-LEDs in thewidth direction of the recording mediums.

In addition, the other configurations regarding the UV-LED units may bereferred to FIG. 4 disclosed in JP-A-2010-23285, and descriptionthereof, for example. Further, the irradiation energy, a light emittingpeak wavelength, and irradiation beam intensity for preliminary curingby the first irradiation units 42 a to 42 e will be described later.

The second irradiation unit 44 irradiates the dots formed on therecording medium S with ultraviolet light to perform (substantially)complete curing, that is, proper curing. The second irradiation unit 44is provided on downstream with respect to the yellow ink head Yin thetransportation direction. In addition, a length of the secondirradiation unit 44 in the width direction of the recording medium S isgreater than a width of the recording medium S. The second irradiationunit 44 irradiates dots formed by each head of the head unit 30 withultraviolet light.

The second irradiation unit 44 of the embodiment includes an UV-LED as alight source of ultraviolet irradiation. Since the UV-LED has beendescribed in the description of the first irradiation units 42 a to 42e, the description thereof will be omitted herein. Herein, as the lightsource, a metal halide lamp, a xenon lamp, a carbon-arc lamp, a chemicallamp, a low-pressure mercury lamp, and a high-pressure mercury lamp canbe used. The irradiation by the lamp is performed to an inner portionsince a light emitting wavelength of a short wavelength is included, andthus, the cured wrinkles are hardly generated, however, on the otherhand, problems occur in various points such as heat generation, size(including cooling device), power consumption, and life time of thelight source, and cost of the irradiator. In addition, compared to thelamps described above, the UV-LED is small in size, has a long lifetime, less heat generation, and high efficiency, and is also excellentin a viewpoint of suppressing cost.

In addition, an irradiation energy, a light emitting peak wavelength,and irradiation peak intensity for proper curing by the secondirradiation unit 44 will be described later.

A rotary encoder (not shown), a paper detecting sensor (not shown), andthe like are included in the detector group 50. The rotary encoderdetects rotation of the upstream transportation roller 23A or thedownstream transportation roller 23B. It is possible to detect atransportation amount of the recording medium S based on the detectionresults of the rotary encoder. The paper detecting sensor detects aposition of an end of the recording medium S which is being fed.

The controller 60 is a control unit which controls the printer. Thecontroller 60 includes an interface unit 61, a CPU 62, a memory 63, anda unit control circuit 64. The interface unit 61 performs transmissionand reception of data between the computer 110 which is an externalapparatus and the printer 1. The CPU 62 is an arithmetic processing unitwhich controls the entire printer. The memory 63 is a memory forsecuring an area for storing programs of the CPU 62 or operation areas,and includes memory elements such as RAM, EEPROM, and the like. The CPU62 controls each unit through the unit control circuit 64, according toprograms stored in the memory 63.

Modification Example of Ink Jet Recording Apparatus

The printer 1 of FIG. 1 described above is only an example of the inkjet recording apparatus according to the embodiment, and there are a lotof variations.

First, the first irradiation units 42 a to 42 e and the secondirradiation unit 44 in FIG. 2 may be any of units for preliminary curingand for proper curing. In a case of discharging the white ink from thewhite ink head W which positions on the upstream of FIG. 2 in thetransportation direction for applying an excellent shielding property toan image to form a solid patterned image, the first irradiation unit 42a is preferable to be an irradiation unit for proper curing.

In addition, the proper curing by the ultraviolet irradiation with theirradiation peak intensity of equal to or more than 800 mW/cm² may beperformed one time, or may be performed two or more times. Among them,in a case of performing the proper curing two or more times, two or morethe second irradiation units 44 may be provided.

In addition, the order of the ink heads of each color shown in FIG. 2may be changed in any order, and only one ink head may be included orone or more ink heads which are not operated may be included. Further,the other ink heads (the colors may be the same as the existing inkheads or may be different) may be included in addition to the ink headsof each color shown in FIG. 2, or any of the ink heads may be changed tothe ink heads of other colors.

Hereinafter, concretization of various variations of the embodiment willbe described as Modification Examples, however, the embodiment is notparticularly limited to Modification Examples.

A recording apparatus according to First Modification Example is theprinter 1 which may not include the second irradiation unit 44 or mayinclude the second irradiation unit 44 which is not operated. Accordingto First Modification Example, one or more irradiation units from thefirst irradiation units 42 a to 42 e perform proper curing instead ofthe second irradiation unit 44, and the preliminary curing describedabove is not performed, in some cases (in a case where all of the firstirradiation units 42 a to 42 e perform proper curing).

A recording apparatus according to Second Modification Example is theprinter 1 which may not include one or more irradiation units from thefirst irradiation units 42 a to 42 e or may include the irradiationunits which are not operated. According to Second Modification Example,the preliminary curing described above is not performed, in some cases(in a case where all of the first irradiation units 42 a to 42 e are notincluded, or where the irradiation units are included but are notoperated).

A recording apparatus according to Third Modification Example is theprinter 1 including one or more head and first irradiation unitsprovided on downstream thereof in the transportation direction, from thewhite ink head W, the black ink head K, the cyan ink head C, the magentaink head M, and the yellow ink head Y, and the first irradiation units42 a to 42 e positioned downstream of each head in the transportationdirection. FIG. 4 shows an aspect of the Third Modification Example, andis a schematic view of the vicinity of the recording areas of the otheraspect of the line printer of FIG. 1. The line printer shown in FIG. 1includes the black ink head K, the first irradiation unit 42 b, and thesecond irradiation unit 44, from the upstream in the transportationdirection.

In addition, the printer 1 of Third Modification Example may not includethe second irradiation unit 44 or may include the second irradiationunit 44 which is not operated in the same manner as First ModificationExample described above, or may not include the first irradiation units42 a to 42 e or may include the irradiation units which are not operatedin the same manner as Second Modification Example described above.

A recording apparatus according to Fourth Modification Example is arecording apparatus including the white ink head W, an irradiation unitfor preliminary curing of white ink, the cyan ink head C, an irradiationunit for preliminary curing of cyan ink, the magenta ink head M, anirradiation unit for preliminary curing of magenta ink, the black inkhead K, an irradiation unit for preliminary curing of black ink, theyellow ink head Y, a first irradiation unit for proper curing, an clearink head CL, and a second irradiation unit for proper curing, from theupstream in transportation direction. According to the recordingapparatus according to Fourth Modification Example, it is possible torealize an excellent shielding property by setting the white ink as abase, and quality improvement of an image by overcoating the clear ink(transparent ink). In addition, before and after discharging the clearink from the clear ink head CL, by emitting ultraviolet light from eachirradiation unit for proper curing, it is possible to perform propercuring of the color ink before discharging the clear ink.

The recording apparatus according to Fourth Modification Example may notinclude at least any of the white ink head W, the irradiation unit forpreliminary curing of white ink, and the clear ink head CL, or mayinclude one irradiation unit for proper curing (is preferable to includethe second irradiation unit for proper curing).

A recording apparatus according to Fifth Modification Example includesan UV-LED not including a condensing lens (hereinafter, also referred toas an “LED with no lens”) as an UV-LED which is an irradiation source ofultraviolet light, instead of the lens-attached LED. The LED with nolens has the same configuration as in the case of the lens-attached LED,except for a point of not including the condensing lens 72 b of FIG. 3.An example of the LED with no lens is formed on a flat surface, otherthan on the surface of the package covering the UV-LED chip 72 a of FIG.3 in a hemispherical shape, and a cover protecting the surface thereofis also formed on a flat surface.

A recording apparatus according to Sixth Modification Example is arecording apparatus which performs pulse irradiation with ultravioletlight by setting input current to LEDs of at least any of the firstirradiation units 42 a to 42 e and the second irradiation unit 44 aspulse current by repeatedly switching the on state and the off state bythe UV-LED driving circuit (not shown) (herein, the LED is also referredto as “pulse irradiation LED”). As a driving circuit of the pulseirradiation LED, an MOF SET circuit or the like which performs PWMcontrol can be used. FIG. 5A is a waveform chart of current which flowsto the UV-LED in a printer of the embodiment, in a case of notperforming pulse irradiation with ultraviolet light. FIG. 5B is awaveform chart of pulse current which flows to the UV-LED in a printerof the embodiment, in a case of performing pulse irradiation withultraviolet light. In a case of the pulse current, the input current ispeak input current which is pulse peak current. The total electricenergy input to the UV-LED is calculated with the following expression.

Total electric energy=input current×T1×Duty ratio

In the expression, irradiation time for the recording medium (T1) meanstime from start of irradiation of the recording medium to the end of theirradiation. Duty ratio is a value expressed in the following expressionwhen performing 1 periodic driving of pulse.

Duty ratio=duration when current is turned on/(duration when current isturned on+duration when current is turned off)

A Duty ratio of the LED which does not perform the pulse irradiationis 1. A Duty ratio in a case of performing the pulse irradiation may be0.5, for example, and a pulse frequency may be set as 1 kHz, forexample. Heat generation of the UV-LED generally becomes greater as thetotal electric energy becomes greater.

The irradiation peak intensity of the UV-LED generally becomes greateras the input current becomes greater. By performing the pulseirradiation as shown in FIG. 5B, in a case of fixing time T1 from thestart of the irradiation to the end of the irradiation, it is possibleto have greater irradiation peak intensity while maintaining the totalinput current. As described above, since the pulse irradiation LEDefficiently increase the irradiation peak intensity, it is particularlysuitable to be used for the second irradiation unit 44 in which greaterirradiation peak intensity is necessary. The pulse irradiation LED mayalso be used in the first irradiation units 42 a to 42 e, and in a caseof performing the proper curing other than the preliminary curing, it ispreferable to use the pulse irradiation LED also for the firstirradiation units.

For example, FIG. 1, FIG. 2, and the description thereof disclosed inJP-A-2006-231795, and description disclosed in JP-T-2011-523370 may bereferred for the pulse irradiation LED described above. The irradiationenergy of the pulse irradiation LED can be calculated using thefollowing expression.

Irradiation energy=irradiation peak intensity×T1×Duty ratio

Accordingly, when T1 is fixed, it is possible to increase the peakintensity while maintaining the same irradiation energy of the LED or itis possible to decrease the irradiation energy of the LED whilemaintaining the same peak intensity, in a case of performing the pulseirradiation, compared to the case of not performing the pulseirradiation.

In addition, the irradiation, particularly the irradiation for propercuring other than the preliminary curing from UV-LED is preferable to beat least any of the pulse irradiation and the spot irradiation. In thiscase, as described above, it is possible to further increase theirradiation peak intensity while maintaining the irradiation energy.

Ink Jet Recording Method

One embodiment of the invention relates to an ink jet recording method.The ink jet recording method can be performed using the ink jetrecording apparatus of the embodiment described above. In addition, theink jet recording method includes a discharging step of dischargingultraviolet curable ink containing vinyl ether group-containing(meth)acrylate esters expressed by the following General Formula (I)(hereinafter, also simply referred to as “vinyl ether group-containing(meth)acrylate esters”), onto a recording medium, and a curing step ofcuring the ultraviolet curable ink which is landed on the recordingmedium by irradiating the ink with ultraviolet light from an ultravioletlight emitting diode (UV-LED) in which peak intensity of the emittedultraviolet light is equal to or more than 800 mW/cm².

Discharging Step

In the discharging step, viscosity of the ink at the time of beingdischarged is preferable to be equal to or less than 25 mPa·s, and morepreferable to be 5 mPa·s to 20 mPa·s. If the viscosity of the ink is asdescribed above when a temperature of the ink is a room temperature orin a state of not heating the ink, the ink may be discharged with atemperature of the ink as a room temperature or without heating the ink.Meanwhile, by heating the ink to a predetermined temperature, the inkmay be discharged by setting the viscosity to a preferable value.Accordingly, excellent discharging stability is realized.

Since ultraviolet curable ink has high viscosity than water-based inkused for ink for normal ink jet, viscosity fluctuation due totemperature fluctuation at the time of discharging is large. Suchviscosity fluctuation of the ink largely affects change of liquiddroplet size and change of liquid droplet discharging speed, andfurther, image quality degradation may occur. Accordingly, it ispreferable to maintain a constant temperature of the ink at the time ofdischarging as much as possible.

Curing Step

Next, in the curing step, the ink which is discharged onto and landed onthe recording medium is cured by irradiation with ultraviolet light(light) from the second irradiation unit 44, or in a case of performingproper curing other than the preliminary curing, from the firstirradiation units 42 a to 42 e. In other words, an ink coating filmformed on the recording medium becomes a cured film by the irradiationwith ultraviolet light. This is because that the photopolymerizationinitiator included in the ink is decomposed by the irradiation withultraviolet light to generate initiating species such as radical, acid,and base, and polymerization reaction of the photopolymerizationcompound is promoted by functions of the initiating species.Alternatively, it is because that the photopolymerization reaction ofthe polymerization compound starts by the irradiation with ultravioletlight. At that time, if there is a sensitizing dye with thephotopolymerization initiator in the ink, the sensitizing dye in asystem absorbs active ultraviolet light to be in an excitation state,and promotes the decomposition of the photopolymerization initiator bybeing in contact with the photopolymerization initiator, and it ispossible to realize curing reaction with higher sensitivity.

The predominance for using the UV-LED as the light source (ultravioletlight source) is as described above.

The light emitting peak wavelength at the time of the irradiation ispreferable to be in a range of 360 nm to 420 nm, and more preferable tobe in a range of 380 nm to 410 nm. It is suitable that the lightemitting peak wavelength be in the range described above, fromviewpoints of easy purchase and low cost of the UV-LED.

In addition, the light emitting wavelength may be one or more in thepreferable wavelength range. Even in a case of the plurality of lightemitting peak wavelength, the entire irradiation energy amount ofultraviolet light having the light emitting peak wavelength is set asthe irradiation energy described above.

The peak intensity (irradiation peak intensity) of the emittedultraviolet light is equal to or more than 800 mW/cm², and preferablyequal to or more than 1000 mW/cm². If the irradiation peak intensity isin the range described above, hardenability is excellent, and it ispossible to effectively prevent generation of cured wrinkles. In moredetail, as a result of delay of the curing of the inner portion of theink coating film compared to the curing of the surface thereof, thesurface of the ink coating film is first cured, and it is possible toeffectively prevent generation of cured wrinkles.

The irradiation peak intensity will be further described. The LEDs havenarrow range of the light emitting wavelength from the characteristicsthereof, and among them, as described above, the long-wavelength LEDhaving the light emitting peak wavelength in a range of 360 nm to 420 nmis obtained with low cost, however includes only a range of the lightemitting wavelength limited by the long-wavelength. Accordingly, it isdifficult for the emitted ultraviolet light to reach the inner portionof the ink droplet which is landed on the recording medium, and only thesurface of the ink coating film is first cured. Thus, the cured wrinklestend to be easily generated. Here, the inventors of the presentapplication have found that it is possible to reduce the cured wrinkleseven in a case of using the long-wavelength LED, by setting theirradiation peak intensity to be equal to or more than 800 mW/cm².Meanwhile, the ultraviolet curable ink containing vinyl ethergroup-containing (meth)acrylate esters expressed by the followingGeneral Formula (I) as the polymerization compound has a high curingspeed, and particularly it is possible to obtain a high curing speed,even with the ultraviolet irradiation from the light source includingthe limited light emitting peak wavelength as the LED. However, in acase of using the ink, the problem in that the cured wrinkles are easilygenerated occurs. The inventors of the present application also foundthat a high-quality recorded material with excellent hardenability andno cured wrinkles can be obtained by setting the irradiation peakintensity to be equal to or more than 800 mW/cm², even in a case ofusing such ink. In a case of using such ink, and when the irradiationpeak intensity is small, the reason of easy generation of the curedwrinkles is expected as slow complete effects in the inner portion ofthe coating film even with the high curing speed with the coating filmsurface with such ink. However, the reason is not limited thereto.

Herein, the ultraviolet irradiation with the irradiation peak intensityof equal to or more than 800 mW/cm² may be performed one time, or may beperformed two or more times. In addition, in a case of performing theultraviolet irradiation two or more times, the ultraviolet irradiationcan be performed plural times from the same light source, or theultraviolet irradiation may be performed one or more times from eachdifferent light source.

In addition, since the irradiation peak intensity can suppress the costof the irradiator and can prevent heat generation or light leakage fromthe light source from affecting the head to obtain excellent dischargingstability, the irradiation peak intensity is preferable to be 800 mW/cm²to 4000 mW/cm², more preferable to be 800 mW/cm² to 2000 mW/cm², andfurther preferable to be 1000 mW/cm² to 2000 mW/cm².

In addition, for the irradiation peak intensity of the presentspecification, a value which is measured using an ultraviolet meterUM-10 and a receptor UM-400 (all manufactured by KONICA MINOLTA SENSING,INC.) is used. However, the measuring method of the irradiation peakintensity is not limited, and a well-known measuring method of therelated art can be used.

In addition, the irradiation energy at the time of the irradiation ispreferable to be 100 mJ/cm² to 600 mJ/cm², more preferable to be 200mJ/cm² to 600 mJ/cm², and further preferable to be 200 mJ/cm² to 500mJ/cm². If the irradiation energy is in the range described above, anexcellent hardenability is obtained, and it is possible to suppress thecost of the irradiation units necessary for the irradiation.

In addition, the irradiation energy of the present specification iscalculated by multiplying the irradiation peak intensity by the timefrom the irradiation start to the irradiation end, and in a case of thepulse irradiation LED, the Duty ratio is further multiplied for thecalculation.

Herein, the ultraviolet irradiation with the irradiation peak intensityof equal to or more than 800 mW/cm² may be performed plural times. Inthis case, the irradiation energy is expressed as the irradiation energyamount obtained by adding the irradiation of the plural times. Inaddition, in a case of performing the irradiation with the irradiationpeak intensity of equal to or more than 800 mW/cm² plural times, forfurther excellent discharging stability, the irradiation energy in theirradiation initially performed after the discharging is preferable tobe equal to or less than 800 mJ/cm², more preferable to be equal to orless than 400 mJ/cm², further preferable to be equal to or less than 200mJ/cm², and further more preferable to be 50 mJ/cm² to 200 mJ/cm².

When the irradiation peak intensity, the irradiation energy, and thelight emitting peak wavelength described above are in the preferableranges, the curing is performed with a low energy and at a high speedwith the composition of the ink which will be described later. Inaddition, it is possible to shorten the irradiation time by thecomposition of the ink which will be described later, and in this case,the recording speed increases. Meanwhile, it is possible to reduce theirradiation peak intensity by the composition of the ink which will bedescribed later, and in this case, the miniaturization of the apparatusand reduction of the cost is realized.

Further, in the curing step, it is preferable to perform preliminarycuring described above, before performing proper curing by emittingultraviolet light from the UV-LED having the irradiation peak intensityof equal to or more than 800 mW/cm² as described above. In the stage ofthe preliminary curing, the ultraviolet light (light) irradiatesultraviolet curable ink which will be described later, from the firstirradiation units 42 a to 42 e for preliminary curing.

The irradiation peak intensity from the UV-LED in the stage of thepreliminary curing is preferable to be less than 800 mW/cm², and morepreferable to be equal to or less than 500 mW/cm², and furtherpreferable to be 100 mW/cm² to 500 mW/cm². In addition, the irradiationenergy in the stage of the preliminary curing is preferable to be equalto or less than 50 mJ/cm², and more preferable to be 10 mJ/cm² to 50mJ/cm². If the irradiation peak intensity and the irradiation energy arein the range described above, it is possible to dispose the light sourcefor irradiation with the irradiation peak intensity of equal to or morethan 800 mW/cm² to be separated from the head, and prevent heatgeneration or light leakage from the light source from affecting thehead to obtain excellent bleed resistance.

Further, in a case of performing multi-color printing with multicolorink by a plurality of heads using the recording apparatus shown in FIG.1, by performing minimum irradiation for preventing color mixing foreach head and finally collectively irradiating the multicolor ink withintensity of equal to or more than 800 mW/cm², it is possible tosuppress the cost of the light source to be extremely low.

In addition, the light emitting peak wavelength in the stage ofpreliminary curing is preferable to be in a range of 360 nm to 420 nm,and more preferable to be in a range of 380 nm to 410 nm, due to thesame reason with the irradiation energy at the time of irradiationdescribed above.

Recording Medium

A recorded material is obtained by discharging the ink onto therecording medium by using the ink jet recording method of theembodiment. As the recording medium, for example, an ink absorbable ornon-absorbable recording medium is used. The ink jet recording method ofthe embodiment can be widely applied to recording media having variousabsorption properties, such as a non-absorbable recording medium inwhich permeation of ink is difficult, and an absorbable recording mediumin which permeation of ink is easy.

As the absorbable recording medium, it is not particularly limited, andfor example, plain paper such as electrophotographic paper having highpermeability of ink, ink jet paper (exclusive paper for ink jetincluding an ink absorbing layer configured of silica particles oralumina particles, or an ink absorbing layer configured of hydrophilicpolymer such as polyvinyl alcohol (PVA) or polyvinylpyrrolidone (PVP)),art paper, coated paper, or cast paper which is used for general offsetprinting having relatively low permeability of ink, or the like, isused.

As the non-absorbable recording medium, it is not particularly limited,and for example, a plastic film or plate such as polyvinyl chloride,polyethylene, polypropylene, polyethylene terephthalate (PET), or thelike, a metallic plate such as iron, silver, copper, aluminum, or thelike, or metallic plate or plastic film obtained by manufacturing byvapor disposition of each metals thereof, alloy plate such as stainlessor brass, or the like is used.

As described above, according to the embodiment, it is possible toprovide an ink jet recording method which can have an excellenthardenability, effectively prevent cured wrinkles, and further haveexcellent abrasion resistance, discharging stability, and bleedresistance.

Ultraviolet Curable Ink

An embodiment of the invention relates to ultraviolet curable ink. Theultraviolet curable ink is used in the ink jet recording method of theembodiment described above.

Hereinafter, an additive (component) which is contained or may becontained in ultraviolet curable ink of the embodiment (hereinafter,simply referred to as “ink”), will be described.

Polymerization Compound

The polymerization compound included in the ink is polymerized at thetime of light irradiation alone or with the operation of thephotopolymerization which will be described later and it is possible tocure printed ink.

Vinyl Ether Group-Containing (Meth)Acrylate Esters

The ink of the embodiment contains vinyl ether group-containing(meth)acrylate esters expressed by the following General Formula (I) asthe polymerization compound.

CH₂═CR¹—COOR²—O—CH═CH—R³  (I)

(In the formula, R¹ represents a hydrogen atom or a methyl group, R²represents a divalent organic residue having 2 to 20 carbon atoms, andR³ represents a hydrogen atom or a monovalent organic residue having 1to 11 carbon atoms.)

By containing vinyl ether group-containing (meth)acrylate estersdescribed above in the ink, it is possible to obtain an excellenthardenability of the ink and to lower viscosity of the ink. Further, itis preferable to use the compound including both vinyl ether group and(meth)acrylic group in one molecular, other than to separately use thecompound including vinyl ester group and the compound including(meth)acrylic group, in a viewpoint of obtaining an excellenthardenability of the ink.

In General Formula (I), as the divalent organic residue having 2 to 20carbon atoms represented by R², a straight, branched, or cyclic alkylenegroup having 2 to 20 carbon atoms which may be substituted, an alkylenegroup including oxygen atoms due to ether bond and/or ester bond in astructure and having 2 to 20 carbon atoms which may be substituted, anda divalent aromatic group having 6 to 11 carbon atoms which may besubstituted are preferable. Among them, an alkylene group having 2 to 6carbon atoms such as an ethylene group, an n-propylene group, anisopropylene group, and a butylene group, and an alkylene group havingoxygen atoms due to ether bond in a structure and having 2 to 9 carbonatoms such as an oxyethylene group, an oxy n-propylene group, an oxyisopropylene group, an oxybutylene group are preferably used.

In General Formula (I), as the monovalent organic residue having 1 to 11carbon atoms represented by R³, a straight, branched, or cyclic alkylgroup having 1 to 10 carbon atoms which may be substituted, and anaromatic group having 6 to 11 carbon atoms which may be substituted arepreferable. Among them, an alkyl group having 1 or 2 carbon atoms suchas a methyl group or an ethyl group, and an aromatic group having 6 to 8carbon atoms such as a phenyl group and a benzene group are preferablyused.

In a case where each organic residue is a group which may besubstituted, the substituent thereof is divided into a group containingcarbon atoms and a group not containing carbon atoms. First, in a casewhere the substituent is a group containing carbon atoms, the number ofthe carbon atoms are counted as the number of carbon atoms in theorganic residue. The group containing carbon atoms is not limited to thefollowing, however, a carboxyl group and an alkoxy group are used, forexample. Next, the group not containing carbon atoms are not limited othe following, however, a hydroxyl group and a halo group are used, forexample.

Vinyl ether group-containing (meth)acrylate esters described above isnot limited to the followings, however, 2-vinyloxyethyl (meth)acrylate,3-vinyloxypropyl (meth)acrylate, 1-methyl-2-vinyloxyethyl(meth)acrylate, 2-vinyloxypropyl (meth)acrylate, 4-vinyloxypropyl(meth)acrylate, 1-methyl-3-vinyloxypropyl (meth)acrylate,1-vinyloxypropyl (meth)acrylate, 2-methyl-3-vinyloxypropyl(meth)acrylate, 1,1-dimethyl-2-vinyloxyethyl (meth)acrylate,3-vinyloxybutyl (meth)acrylate, 1-methyl-2-vinyloxypropyl(meth)acrylate, 2-vinyloxybutyl (meth)acrylate, 4-vinyloxycyclohexyl(meth)acrylate, 6-vinyloxycyclohexyl (meth)acrylate,4-vinyloxymethylcyclohexylmethyl (meth)acrylate,3-vinyloxymethylcyclohexylmethyl (meth)acrylate,2-vinyloxymethylcyclohexylmethyl (meth)acrylate,p-vinyloxymethylphenylmethyl (meth)acrylate,m-vinyloxymethylphenylmethyl (meth)acrylate,o-vinyloxymethylphenylmethyl (meth)acrylate, 2-(vinyloxyethoxy) ethyl(meth)acrylate, 2-(vinyloxyisopropoxy) ethyl (meth)acrylate,2-(vinyloxyethoxy) propyl (meth)acrylate, 2-(vinyloxyethoxy) isopropyl(meth)acrylate, 2-(vinyloxyisopropoxy) propyl (meth)acrylate,2-(vinyloxyisopropoxy) isopropyl (meth)acrylate, 2-(vinyloxyethoxy)ethyl (meth)acrylate, 2-(vinyloxyethoxy isopropoxy) ethyl(meth)acrylate, 2-(vinyloxyisopropoxy ethoxy) ethyl (meth)acrylate,2-(vinyloxyisopropoxyisopropoxy) ethyl (meth)acrylate, 2-(vinyloxyethoxy ethoxy) propyl (meth)acrylate, 2-(vinyloxy ethoxyisopropoxy)propyl (meth)acrylate, 2-(vinyloxyisopropoxyethoxy) propyl(meth)acrylate, 2-(vinyloxyisopropoxyisopropoxy) propyl (meth)acrylate,2-(vinyloxyethoxyethoxy) isopropyl (meth)acrylate, 2-(vinyloxyethoxyisopropoxy) isopropyl (meth)acrylate, 2-(vinyloxy isopropoxyethoxy)isopropyl (meth)acrylate, 2-(vinyloxyisopropoxyisopropoxy) isopropyl(meth)acrylate, 2-(vinyloxyethoxyethoxyethoxy) ethyl (meth)acrylate,2-(vinyloxyethoxyethoxyethoxyethoxy) ethyl (meth)acrylate,2-(isopropenoxyethoxy) ethyl (meth)acrylate,2-(isopropenoxyethoxyethoxy) ethyl (meth)acrylate,2-(isopropenoxyethoxyethoxyethoxy) ethyl (meth)acrylate,2-(isopropenoxyethoxyethoxyethoxyethoxy) ethyl (meth)acrylate,polyethylene glycol monovinylether (meth)acrylate, and polypropyleneglycol monovinylether (meth)acrylate are used, for example.

Among them, since the lower viscosity of the ink, a high flash point,and an excellent hardenability of ink can be obtained, 2-(vinyloxyetoxy)ethyl (meth)acrylate, that is, at least any of 2-(vinyloxyetoxy) ethylacrylate and 2-(vinyloxyetoxy) ethyl methacrylate is preferable, and2-(vinyloxyetoxy) ethyl acrylate is more preferable. Particularly, sinceall of 2-(vinyloxyetoxy) ethyl acrylate and 2-(vinyloxyetoxy) ethylmethacrylate have simple structure and small molecular weight, it ispossible to significantly lower viscosity of ink. As 2-(vinyloxyetoxy)ethyl (meth)acrylate, 2-(2-vinyloxyetoxy) ethyl (meth)acrylate and2-(1-vinyloxyetoxy) ethyl (meth)acrylate are used, and as2-(vinyloxyetoxy) ethyl acrylate, 2-(2-vinyloxyetoxy) ethyl acrylate and2-(1-vinyloxyetoxy) ethyl acrylate are used. In addition,2-(vinyloxyetoxy) ethyl acrylate is more excellent in viewpoint ofhardenability, compared to 2-(vinyloxyetoxy) ethyl methacrylate.

Vinyl ether group-containing (meth)acrylate esters may be used alone, ormay be used in combination of two or more kinds.

The content of vinyl ether group-containing (meth)acrylate esters,particularly 2-(vinyloxyetoxy) ethyl (meth)acrylate, is preferable to be10% by mass to 90% by mass, more preferable to be 20% by mass to 80% bymass, further preferable to be 20% by mass to 70% by mass, and even morepreferable to be 20% by mass to 60% by mass, with respect to the totalcontent (100% by mass) of the ink. If the content thereof is equal to ormore than 10% by mass, it is possible to lower the viscosity of the inkand to obtain excellent hardenability of the ink. Meanwhile, if thecontent thereof is equal to or less than 90% by mass, it is possible tomaintain preservation stability of the ink in an excellent state and tofurther effectively prevent generation of the cured wrinkles.

As a manufacturing method of vinyl ether group-containing (meth)acrylateesters described above, it is not limited to the following, however, amethod of esterifying (meth)acrylate and hydroxyl group-containing vinylether (manufacturing method B), a method of esterifying halide(meth)acrylate and hydroxyl group-containing vinyl ether (manufacturingmethod C), a method of esterifying (meth)acrylic anhydride and hydroxylgroup-containing vinyl ether (manufacturing method D), a method ofesterifying (meth)acrylic ester and hydroxyl group-containing vinylether (manufacturing method E), a method of esterifying (meth)acrylateand halogen-containing vinyl ether (manufacturing method F), a method ofesterifying (meth)acrylate alkali (earth) metal salt andhalogen-containing vinyl ether (manufacturing method G), a method oftransvinylation of hydroxyl group-containing (meth)acrylic ester andvinyl carboxylic acid (manufacturing method H), a method oftransetherification of hydroxyl group-containing (meth)acrylic ester andalkyl vinyl ether (manufacturing method I) are used.

Among them, the manufacturing method E is preferable since it ispossible to excellently exhibit desirable effects of the embodiment.

Other Polymerization Compounds

As polymerization compounds other than the described above compounds(hereinafter, referred to as “other polymerization compounds”), variousmonofunctional, bifunctional, and trifunctional or more ofpolyfunctional monomers and oligomers which are well known in therelated art can be used. As the monomer, unsaturated carboxylic acidsuch as (meth)acrylate, itaconate, crotonate, isocrotonic acid, andmaleic acid, or salt thereof, ester, urethane, amide, and anhydridethereof, acrylonitrile, styrene, various unsaturated polyester,unsaturated polyether, polyether polyamides, and unsaturated urethane,are used for example.

In addition, as the oligomers, an oligomer formed from the monomersdescribed above such as a straight-chain acrylic oligomer or the like,epoxy (meth)acrylate, oxetane (meth)acrylate, aliphatic urethane(meth)acrylate, aromatic urethane (meth)acrylate, and polyester(meth)acrylate are used for example.

In addition, as the other monofunctional monomer or multifunctionalmonomer, an N-vinyl compound may be contained. As the N-vinyl compound,N-vinyl formamide, N-vinyl carbazole, N-vinyl acetamide, N-vinylpyrrolidone, N-vinyl caprolactam, and acryloylmorpholine, andderivatives thereof are used, for example.

Among the other polymerization compounds, ester of (meth)acrylate, thatis, (meth)acrylate is preferable.

Among the (meth)acrylate, as monofunctional (meth)acrylate,monofunctional (meth)acrylate having an aromatic ring skeleton such asisoamyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate,octyl (meth)acrylate, decyl (meth)acrylate, isomyristyl (meth)acrylate,isostearyl (meth)acrylate, 2-ethylhexyl-diglycol (meth)acrylate,2-hydroxy butyl (meth)acrylate, butoxyethyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxy diethylene glycol(meth)acrylate, methoxy polyethylene glycol (meth)acrylate, methoxypropylene glycol (meth)acrylate, phenoxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobornyl (meth)acrylate, 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl (meth)acrylate,2-hydroxy-3-phenoxypropyl (meth)acrylate, lactone-modified flexible(meth)acrylate, t-butyl cyclohexyl (meth)acrylate, dicyclopentanyl(meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, and benzyl(meth)acrylate are used. Among them, one or more selected from a groupconsisting of phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, andisobornyl (meth)acrylate are preferable.

Among (meth)acrylate described above, as bifunctional (meth)acrylate,diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate,tetraethylene glycol di(meth)acrylate, polyethylene glycoldi(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropyleneglycol di(meth)acrylate, polypropylene glycol di(meth)acrylate,1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate,1,9-nonanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate,dimethylol-tricyclodecane di(meth)acrylate, bisphenol A EO (ethyleneoxide) adduct di(meth)acrylate, bisphenol A PO (propylene oxide) adductdi(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate,and polytetramethyleneglycol di(meth)acrylate are used, for example.Among them, dipropylene glycol di(meth)acrylate is preferable.

Among (meth)acrylate described above, as trifunctional or more ofpolyfunctional (meth)acrylate, trimethylolpropane tri(meth)acrylate,EO-modified trimethylolpropane tri(meth)acrylate, pentaerythritoltri(meth)acrylate, pentaerythritol tetra(meth)acrylate,dipentaerythritol hexa(meth)acrylate, ditrimethylol propanetetra(meth)acrylate, glycerine propoxy tri(meth)acrylate,caprolactone-modified trimethylolpropane tri(meth)acrylate,pentaerythritol tetra(meth)acrylate, and caprolactam-modifieddipentaerythritol hexa(meth)acrylate are used, for example.

Among them, since advantageous effects described below are obtained, theink of the embodiment is preferable to contain at least any ofmonofunctional (meth)acrylate and bifunctional or more (meth)acrylate,more preferable to contain monofunctional (meth)acrylate, and furtherpreferable to contain both thereof. In this case, low viscosity of inkis obtained, excellent solubility of the photopolymerization initiatorand the other additive is obtained, excellent discharging stability atthe time of ink jet recording is easily obtained, and further hightoughness, heat resistance, and chemical resistance of the coating filmare increased. In addition, since the hardenability and the solubilityof the initiator become more excellent, monofunctional (meth)acrylateincluding an aromatic skeleton in the molecule such as phenoxyethyl(meth)acrylate, benzyl (meth)acrylate, 2-hydroxyphenoxypropyl(meth)acrylate, and phenoxydiethylene glycol (meth)acrylate ispreferable, among monofunctional (meth)acrylate. In addition, since thehardenability and the abrasion resistance of the coating film becomemore excellent, one or more selected from a group consisting ofdiethylene glycol di(meth)acrylate, tripropylene glycoldi(meth)acrylate, and dipropyleneglycoldi(meth)acrylate are preferable,among bifunctional (meth)acrylate.

The other polymerization compound may be used alone or may be used incombination of two or more kinds.

In a case of containing the other polymerization compound, the contentthereof is preferable to be 5% by mass to 85% by mass, and morepreferable to be 15% by mass to 70% by mass, with respect to the totalcontent (100% by mass) of the ink. Since excellent hardenability due tosolubility of the photopolymerization initiator, viscosity reduction,and preservation stability are obtained, the content of monofunctional(meth)acrylate except for vinyl ether group-containing (meth)acrylateesters described above is preferable to be 5% by mass to 50% by mass,and more preferable to be 10% by mass to 40% by mass, with respect tothe total content (100% by mass) of the ink.

Since the excellent hardenability, the abrasion resistance, and theadhesiveness are obtained, the content of bifunctional or more(meth)acrylate is preferable to be 5% by mass to 55% by mass, and morepreferable to be 10% by mass to 40% by mass, with respect to the totalcontent (100% by mass) of the ink.

Photopolymerization Initiator

The ink of the embodiment contains the photopolymerization initiator.The photopolymerization initiator is used for performing printing bycuring the ink existing on a surface of a recording medium withpolymerization by the irradiation with ultraviolet light. By usingultraviolet light (UV), it is possible to obtained excellent safety andto suppress cost of a light source lamp. The photopolymerizationinitiator is not limited as long as active species of radical or cationare generated and polymerization of the polymerization compound isinitiated by the energy of the light (ultraviolet light), however, aphotoradical polymerization initiator or a photocation polymerizationinitiator can be used, and among them, it is preferable to use thephotoradical polymerization initiator.

As the photoradical polymerization initiator, aromatic ketones, acylphosphine oxide compounds, aromatic onium salt compounds, organicperoxides, thio compounds (such as thioxanthone compounds, thiophenylgroup-containing compounds), α-aminoalkylphenone compounds,hexaarylbiimidazole compounds, ketoxime ester compounds, boratecompounds, azinium compounds, metallocene compounds, active estercompounds, compounds having carbon-halogen bond, and alkylaminecompounds are used, for example.

Among them, since it is possible to realize further excellenthardenability of the ink, thioxanthone compounds are preferable, andcombination of acyl phosphine oxide compounds and thioxanthone compoundsis more preferable.

As detailed examples of the photoradical polymerization initiator,acetophenone, acetophenone benzyl ketal, 1-hydroxy cyclohexyl phenylketone, 2,2-dimethoxy-2-phenylacetophenone, xanthone, fluorenone,benzaldehyde, fluorene, anthraquinone, triphenylamine, carbazole,3-methylacetoacetate phenone, 4-chloro benzophenone,4,4′-dimethoxy-benzophenone, 4,4′-diamino benzophenone, Michler'sketone, benzoin propyl ether, benzoin ethyl ether, benzyl dimethylketal, 1-(4-isopropyl-phenyl)-2-hydroxy-2-methyl-propan-1-one,2-hydroxy-2-methyl-1-phenyl propan-1-one, thioxanthone, diethylthioxanthone, 2-isopropylthio xanthone, 2-chlorothioxanthone,2-methyl-1-[4-(methylthio) phenyl]-2-morpholino-propan-1-one, bis(2,4,6-trimethyl benzoyl)-phenyl phosphine oxide, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, 2,4-diethyl thioxanthone, andbis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxide areused.

As commercially available products of the photoradical polymerizationinitiator, IRGACURE 651 (2,2-dimethoxy-1,2-diphenyl ethane-1-one),IRGACURE 184 (1-hydroxy-cyclohexyl-phenyl-ketone), DAROCUR 1173(2-hydroxy-2-methyl-1-phenyl-propan-1-one), IRGACURE 2959(1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one),IRGACURE 127 (2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]phenyl}-2-methyl-propane-1-one), IRGACURE 907(2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one), IRGACURE 369(2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1), IRGACURE379 (2-(dimethylamino)-2-[(4-methylphenyl) methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone), DAROCUR TPO(2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide), IRGACURE 819 (bis(2,4,6-trimethyl benzoyl)-phenyl phosphine oxide), IRGACURE 784 (bis(η5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)-phenyl) titanium), IRGACURE OXE 01(1,2-octane dione, 1-[4-(phenylthio)-, 2-(O-benzoyloxime)]), IRGACUREOXE 02 (ethanone, 1-[9-ethyl-6-(2-methyl-benzoyl)-9H-carbazol-3-yl]-,1-(O-acetyl oxime)), IRGACURE 754 (mixture of oxyphenyl acetic acid,2-[2-oxo-2-phenylacetoxy ethoxy] ethyl ester and oxyphenyl acetic acid,and 2-(2-hydroxyethoxy) ethyl ester) (all manufactured by BASF),Speedcure TPO, Speedcure DETX (2,4-diethyl thioxanthone), Speedcure ITX(2-isopropylthioxanthone) (all manufactured by Lambson), KAYACURE DETX-S(2,4-diethyl thioxanthone) (manufactured by Nippon Kayaku Co., Ltd.),Lucirin TPO, LR8893, LR8970 (all manufactured by BASF), and UBECRYL P36(manufactured by UCB) are used, for example.

The photopolymerization initiator may be used along or may be used incombination of two or more kinds.

The content of the photopolymerization initiator is preferable to be 5%by mass to 15% by mass and more preferable to be 7% by mass to 13% bymass, with respect to the total content (100% by mass) of the ink. Ifthe content thereof is in the range described above, it is possible tosufficiently exhibit the ultraviolet curing speed, and to avoid residueof dissolved photopolymerization initiator or coloring due to theinitiator. It is preferable to contain acyl phosphine oxide compoundsamong the photopolymerization initiator. The content of acyl phosphineoxide compounds described above is preferable to be 5% by mass to 15% bymass and more preferable to be 7% by mass to 13% by mass, with respectto the total content (100% by mass) of the ink.

In addition, by using the photopolymerization compound as thepolymerization compound described above, it is possible to omit theaddition of the photopolymerization initiator, however, it is suitableto use the photopolymerization initiator since it is possible to easilyadjust the start of the polymerization.

Color Material

The ink may further contain color materials. As the color material, atleast one of a pigment and a dye can be used.

Pigment

By using the pigment as the color material, it is possible to obtainexcellent light resistance of the ink. Both an inorganic pigment and anorganic pigment can be used for the pigment.

As the inorganic pigment, carbon blacks (C.I. Pigment Black 7) such asfurnace black, lamp black, acetylene black, and channel black, ironoxide, titanium oxide can be used.

As the organic pigment, azo pigments such as insoluble azo pigments,condensed azo pigments, azo lake, and chelate azo, polycyclic pigmentssuch as phthalocyanine pigments, perylene and perinone pigments,anthraquinone pigments, quinacridone pigments, dioxane pigments,thioindigo pigments, isoindolinone pigments, and quinophthalonepigments, dye chelate (for example, basic dye chelate, acidic dyechelate, or the like), dye lake (basic dye lake, acidic dye lake, or thelike), nitro pigments, nitroso pigments, aniline black, and daylightfluorescent pigments are used.

In more detail, as carbon black used for the black ink, No. 2300, No.900, MCF88, No. 33, No. 40, No. 45, No. 52, MA7, MA8, MA100, No. 2200Band the like (all manufactured by Mitsubishi Chemical Corporation),Raven 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255, Raven 700and the like (all manufactured by Carbon Columbia), Regal 400R, Regal330R, Regal 660R, Mogul L, Monarch 700, Monarch 800, Monarch 880,Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400, andthe like (all manufactured by CABOT JAPAN K.K.), Color Black FW1, ColorBlack FW2, Color Black FW2V, Color Black FW18, Color Black FW200, ColorBlack S150, Color Black S160, Color Black 5170, Printex 35, Printex U,Printex V, Printex 140U, Special Black 6, Special Black 5, Special Black4A, Special Black 4 (all manufactured by Degussa), and Microlith Black0066 K (former Microlith Black C-K, manufactured by BASF) are used.

As the pigment used for the white ink, C.I. Pigment White 6, 18, and 21are used.

As the pigment used for the yellow ink, C.I. Pigment Yellow 1, 2, 3, 4,5, 6, 7, 10, 11, 12, 13, 14, 16, 17, 24, 34, 35, 37, 53, 55, 65, 73, 74,75, 81, 83, 93, 94, 95, 97, 98, 99, 108, 109, 110, 113, 114, 117, 120,124, 128, 129, 133, 138, 139, 147, 151, 153, 154, 167, 172, and 180 areused.

As the pigment used for the magenta ink, C.I. Pigment Red 1, 2, 3, 4, 5,6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30, 31, 32,37, 38, 40, 41, 42, 48(Ca), 48(Mn), 57(Ca), 57:1, 88, 112, 114, 122,123, 144, 146, 149, 150, 166, 168, 170, 171, 175, 176, 177, 178, 179,184, 185, 187, 202, 209, 219, 224, and 245, or C.I. Pigment Violet 19,23, 32, 33, 36, 38, 43, and 50 are used.

As the pigment used for the cyan ink, C.I. Pigment Blue 1, 2, 3, 15,15:1, 15:2, 15:3, 15:34, 15:4, 16, 18, 22, 25, 60, 65, and 66, and C.I.Vat Blue 4 and 60 are used.

In addition, as the pigment other than magenta, cyan, and yellow, C.I.Pigment Green 7 and 10, C.I. Pigment Brown 3, 5, 25, and 26, C.I.Pigment Orange 1, 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, and63 are used.

The pigment may be used alone, or may be used in combination of two ormore kinds.

In a case of using the pigment described above, an average particle sizethereof is preferable to be equal to or less than 300 nm and morepreferable to be 50 nm to 200 nm. If the average particle size thereofis in the range described above, it is possible to obtain furtherexcellent reliability such as discharging stability or dispersionstability of the ink, and to form an image with excellent image quality.Herein, the average particle size of the embodiment is measured with adynamic light scattering method.

Dye

A dye can be used as the color material. As the dye, it is notparticularly limited, and an acidic dye, a direct dye, a reactive dye,and a basic dye can be used. As the dye, C.I. Acid Yellow 17, 23, 42,44, 79, and 142, C.I. Acid Red 52, 80, 82, 249, 254, and 289, C.I. AcidBlue 9, 45, and 249, C.I. Acid Black 1, 2, 24, and 94, C.I. Food Black 1and 2, C.I. Direct Yellow, 1, 12, 24, 33, 50, 55, 58, 86, 132, 142, 144,and 173, C.I. Direct Red 1, 4, 9, 80, 81, 225, and 227, C.I. Direct Blue1, 2, 15, 71, 86, 87, 98, 165, 199, and 202, C.I. Direct Black 19, 38,51, 71, 154, 168, 171, and 195, C.I. Reactive Red 14, 32, 55, 79, and249, C.I. Reactive Black 3, 4, and 35 are used, for example.

The dye described above may be used alone, or may be used in combinationof two or more kinds.

Since excellent shielding property and color reproducibility areobtained, the content of the color material is preferable to be 1% bymass to 20% by mass with respect to the total content (100% by mass) ofthe ink.

Dispersant

When the ink contains the pigment, the ink may further contain adispersant for obtaining further excellent pigment dispersibility. Asthe dispersant, it is not particularly limited, and a dispersant whichis commonly used for preparing a pigment dispersion liquid such as apolymer dispersant, is used. As detailed examples, a dispersantincluding one or more of polyoxyalkylene polyalkylene polyamine, vinylpolymer and copolymer, acrylic polymer and copolymer, polyester,polyamide, polyimide, polyurethane, amino-based polymer,silicon-containing polymer, sulfur-containing polymer,fluorine-containing polymer, and epoxy resin, as main components, areused. As commercially available products of the polymer dispersant,Ajisper Series manufactured by Ajinomoto Fine-Techno Co., Inc.,Solsperse Series (such as Solsperse 36000) which can be purchased fromAvecia or Noveon, DISPERBYK Series manufactured by BYK Chemie, andDISPARLON Series manufactured by Kusumoto Chemicals, Ltd. are used.

Slip Agent

The ink of the embodiment may further contain a slip agent (surfactant).As the slip agent, it is not particularly limited, and as silicone basedsurfactant, polyester-modified silicone or polyether-modified siliconecan be used, for example, and it is particularly preferable to usepolyester-modified polydimethylsiloxane or a polyether modifiedpolydimethylsiloxane. As detailed example, BYK-347, BYK-348, BYK-UV3500,3510, 3530, and 3570 (all manufactured by BYK) can be used.

The slip agent may be used alone and may be used in combination of twoor more kinds. In addition, the content of the slip agent is notlimited, and a preferable amount may be suitably added.

Other Additives

The ink may further contain additives (components) other than theadditives described above. As such component, it is not particularlylimited, and a polymerization accelerator, a polymerization inhibitor, apermeation accelerator, and a wetting agent (moisturizing agent) whichare well known in the related art may be used, for example. As the otheradditives, a fixing agent, an antifungal agent, a preservative, anantioxidant, an ultraviolet absorbing agent, a chelate, pH adjuster, anda thickener which are well known in the related art may be used, forexample.

EXAMPLES

Hereinafter, the embodiment of the first invention will be described inmore detail with reference to Examples, however, the embodiment is notlimited only to Examples.

Used Raw Material

Raw materials used for Examples and Comparative Examples are as follows.

Coloring Materials (pigments)

-   -   Novoperm Yellow 4G01 (C.I. Pigment Yellow 155, manufactured by        Clariant, hereinafter referred to as “PY 155”)    -   IRGALITE BLUE GLVO (C.I. Pigment Blue 15:4, manufactured by        BASF, hereinafter referred to as “PB 15:4”)    -   CROMOPHTAL PinkPT (SA) (C.I. Pigment Red 122, manufactured by        BASF, hereinafter referred to as “PR 122”)

Dispersant

-   -   Solsperse 36000 (product name, manufactured by Lubrizol        Corporation, hereinafter referred to as “SOL 36000”)

Radical Polymerization Compounds

-   -   VEEA (2-(2-vinyloxy ethoxy) ethyl acrylate, product name,        manufactured by Nippon Shokubai Co., Ltd., hereinafter referred        to as “VEEA”)    -   Viscoat #192 (phenoxyethyl acrylate, product name, manufactured        by OSAKA ORGANIC CHEMICAL INDUSTRY LTD., hereinafter, referred        to as “PEA”)    -   SR 230 (diethylene glycol diacrylate, product name, manufactured        by Sartomer Company Inc., hereinafter, referred to as “DEGDA”)    -   APG-200 (tripropylene glycol diacrylate, product name,        manufactured by SHIN-NAKAMURA CHEMICAL CO., LTD., hereinafter,        referred to as “TPGDA”)    -   IBXA (isobornyl acrylate, product name, manufactured by OSAKA        ORGANIC CHEMICAL INDUSTRY LTD., hereinafter, referred to as        “MX”)    -   V #160 (benzyl acrylate, product name, manufactured by OSAKA        ORGANIC CHEMICAL INDUSTRY LTD., hereinafter, referred to as        “BZA”)

Radical Photopolymerization Initiators

-   -   IRGACURE 819 (product name, manufactured by BASF, solid content        of 100%, hereinafter, referred to as “819”)    -   DAROCURE TPO (product name, manufactured by BASF, solid content        of 100%, hereinafter, referred to as “TPO”)

Slip Agent

-   -   BYK-UV3500 (product name, manufactured by BYK, hereinafter,        referred to as “UV3500”) Examples 1 to 13, Comparative Examples        1 to 6, and Reference Examples 1 to 6

Manufacture of Pigment Dispersion Liquid

A pigment dispersion liquid was manufactured before manufacturing theink. 2 parts by mass of each pigment, 0.6 parts by mass of dispersant,and 20 parts by mass of polymerization compound as a dispersion medium,were mixed, and stirred with a stirrer for 1 hour. The mixed liquidafter stirring was dispersed with a bead mill, and pigment dispersionliquid was obtained. In addition, as dispersion conditions, zirconiabeads having a diameter of 0.65 mm were filled with a filling rate of70%, a circumferential speed was set to be 9 mm/s, dispersion time wasset to be 2 to 4 hours. The dispersion medium was used with thepolymerization compounds which can be used for each ink, in priorityorder of PEA, BZA, IBX, and VEEA.

Manufacture of Ultraviolet Curable Ink 1 to 8

Components disclosed in Table 1 below were added to have compositionsdisclosed in Table 1 below (unit is % by mass) and were stirred by ahigh-speed water-cooling type stirrer, and thus, ultraviolet curableyellow ink, ultraviolet curable cyan ink, and ultraviolet curablemagenta ink (1 to 8) were prepared. In addition, in Table 1,transmittance (unit is %) at a wavelength of 395 nm was obtained bydiluting each ultraviolet curable ink with ethyl diglycol acetate by1000 times, and measuring the diluted solution with a spectrophotometerU3300 (product name manufactured by Hitachi, Ltd.).

TABLE 1 Ink 1 to 8 Ink No. Component 1 2 3 4 5 6 7 8 VEEA 15.00 15.00 15.00 15.00  15.00 20.00  15.00  20.00  PEA 30.00 30.00  30.00 — —68.20  — 68.20  BZA — — — 30.00  — — 30.00  — IBX — — — — 30.00 — — —DEGDA 25.20 25.20  25.20 25.20  25.20 — 25.20  — TPGDA 18.00 18.00 18.00 18.00  18.00 — 18.00  — PY 155 2.00 — — 2.00 2.00 2.00 — — PB 15:4— 2.00 — — — — 2.00 2.00 PR 122 — — 2.00 — — — — — SOL 36000 0.60 0.600.60 0.60 0.60 0.60 0.60 0.60 819 5.00 5.00 5.00 5.00 5.00 5.00 5.005.00 TPO 4.00 4.00 4.00 4.00 4.00 4.00 4.00 4.00 UV 3500 0.20 0.20 0.200.20 0.20 0.20 0.20 0.20 Total 100.00 100.00  100.00 100.00  100.00100.00  100.00  100.00  Transmittance 0.37 7.64 4.30 0.37 0.37 0.37 7.647.64 at a wavelength of 395 nm (%) Ink hardenability B A A B C C A B

Ink Jet Recording of Examples 1

Ink jet recording was performed using the printer 1 which is a lineprinter in FIG. 4 described above. In detail, in the printer 1, the headwas filled with the ultraviolet curable yellow ink 1 prepared asdescribed above. Nozzle density of the head was set to be 720 dpi. Asolid patterned image having a film thickness of 10 μm was printed on aPET film (product name: PET 50A, manufactured by Lintec Corporation)which is a recording medium, with conditions of recording resolution of720 dpi×720 dpi, Duty of 100%, liquid droplet weight of 7 ng, and onepass (single pass). The printing was performed by heating the ink sothat the viscosity of the ink is 10 mPa·s. In addition, the “solidpatterned image” in the present specification means an image on whichdots are recorded with respect to all pixels each of which is a minimumrecording unit area specified by the recording resolution.

With the recording, in order to cure the image, ultraviolet light havingirradiation peak intensity of 800 mW/cm² (see Table 2 below), inputcurrent of LEDs of 230 mA (for each UV-LED), and a light emitting peakwavelength of 395 nm was emitted for predetermined time, from thelens-attached LED (described above) in the ultraviolet irradiationdevice installed on downstream of the recording medium in thetransportation direction, that is, the first irradiation unit 42 f. Theirradiation energy at that time was 400 mJ/cm² (see Table 2 below).Accordingly, the ink jet recording was performed, and a recordedmaterial was obtained.

In addition, the irradiation peak intensity of each example which willbe described later were adjusted by changing the input current of theUV-LED, and were measured with a distance from a light emitting surfaceto the recording medium. Further, the irradiation energy is a valuecalculated from the sum of the irradiation peak intensity [mW/cm²] andthe irradiation time [s]. In the printing, each irradiation unit 42 and44 continued irradiation, and the irradiation duration when one pointfrom the irradiated surface of the recording medium which is transportedunder the irradiation units passes the irradiation area irradiated bythe irradiation units were set as the irradiation time T1. Theirradiation time T1 was adjusted by changing the number of the UV-LEDswhich emit light from the plurality of UV-LEDs arranged in thetransportation direction of the recording medium in the irradiationunit. Other irradiation units were not used.

Ink Jet Recording of Examples 2 to 4, and 10 to 13, Comparative Examples1, 4, and 5, and Reference Examples 1 to 6

The ink jet recording was performed in the same manner as Example 1except for setting the irradiation peak intensity, irradiation energy,and the ink filled the head as shown in Tables 2 to 4, and a recordedmaterial was obtained.

Ink Jet Recording of Examples 5 to 7, and Comparative Examples 2 and 3

The ink jet recording was performed in the same manner as Example 1except for using the second irradiation unit 44 in addition to the firstirradiation unit 42 f or using the second irradiation unit 44 withoutusing the first irradiation unit 42 f, and setting the irradiation peakintensity, irradiation energy, and the ink filled the head as shown inTables 2 to 4, and a recorded material was obtained.

Ink Jet Recording of Example 8

The ink jet recording was performed in the same manner as Example 1except for using the LED with no lens (described above) instead of thelens-attached LED for the LED in the first irradiation unit 42 f, andsetting the irradiation peak intensity and irradiation energy as shownin Table 2, and a recorded material was obtained. The irradiation timeT1 was the same as Example 1. The input current of the LED was necessaryto be 270 mA.

Ink Jet Recording of Example 9

The ink jet recording was performed in the same manner as Example 1except for using the LED with no lens which is the pulse irradiation LED(described above) instead of the lens-attached LED for the LED in thefirst irradiation unit 42 f, and setting the irradiation peak intensityand irradiation energy as shown in Table 2, and a recorded material wasobtained. In the pulse irradiation LED, the Duty ratio was set to 0.5,the pulse frequency was set to 1 kHz, and the input current was set to220 mA. The irradiation time T1 was the same as Example 1.

Ink Jet Recording of Comparative Example 6

The ink jet recording was performed using the serial printer shown inFIG. 6. In detail, in the serial printer shown in FIG. 6, the head isfilled with ultraviolet curable ink 1 shown in Table 4. The nozzledensity of the head was set to be 360 dpi. A solid patterned imagehaving a film thickness of 10 μm was printed on a PET film (productname: PET 50A, manufactured by Lintec Corporation) which is a recordingmedium, with conditions of recording resolution of 720 dpi×720 dpi, Dutyof 100%, liquid droplet weight of 7 ng, and 4 passes (2 passes in themain scanning direction×2 passes in the auxiliary scanning direction).

With the recording, in order to cure the image, ultraviolet light havingirradiation peak intensity of 500 mW/cm² (see Table 2 below) and a lightemitting peak wavelength of 395 nm was emitted for predetermined time,from the lens-attached LED (described above) in the ultravioletirradiation device installed on downstream of the recording medium inthe transportation direction, that is, the first irradiation units 92 aand 92 b. The irradiation energy for one pass was set to be 200 mJ/cm².Accordingly, the ink jet recording was performed, and a recordedmaterial was obtained.

Evaluation Items

For the recorded materials obtained in respective Examples (includingExamples 14 to 23 which will be described later) and ComparativeExamples (including Comparative Example 7 will be described later),hardenability, cured wrinkles, abrasion resistance, bleed resistance,and discharging stability were evaluated with the following methods.

1. Hardenability Test 1

After rubbing the surface of the obtained solid patterned image(recorded surface) using a Johnson cotton swab manufactured by Johnson &Johnson, with 40 times of reciprocation and a load of 10 g, it wasdetermined whether or not there were scratches on the recorded surface,and the hardenability at the time of the printing was evaluated.Evaluation criteria are as follows. The evaluation results are shown inTables 2 to 5.

O: No scratchesX: Scratches generated

2. Hardenability Test 2

When obtaining a cured coating film having a thickness of 10 μm byfurther coating the PET film (PET 50A) with each ink by a bar coater andcuring by emitting light by the UV-LED having the irradiation peakintensity of 800 mW/cm² and the light emitting peak wavelength of 395nm, the surface was rubbed with the conditions same as HardenabilityTest 1, and irradiation energy necessary to have “0” of the evaluationcriteria in Hardenability Test 1 was evaluated. The evaluation resultswere shown in Table 1 as “ink hardenability”.

A: Equal to or less than 100 mJ/cm²B: More than 100 mJ/cm² and equal to or less than 150 mJ/cm²C: More than 150 mJ/cm²

3. Cured Wrinkles

For surface roughness of the recording medium, a root mean square height(Rq value) was measured by using a laser microscope VK-9700(manufactured by KEYENCE), and the recorded surface was visuallyobserved.

Evaluation criteria are as follows. The evaluation results are shown inTables 2 to 5.

O: Rq was equal to or less than 3. Sufficient shiny appearance wasobserved when seen reflected light of the film.Δ: Rq exceeded 3 or was equal to or less than 5. Slightly insufficientshiny appearance was observed when seen reflected light of the film.X: Rq exceeded 5. Shiny appearance was insufficient and the surface wasobserved to be rough when seen reflected light of the film.

4. Abrasion Resistance

Evaluation of abrasion resistance was performed using a Color FastnessRubbing Tester (manufactured by TESTER SANGYO CO., LTD.), based on JISK5701 (ISO 11628) (regulation of a method for testing ink, a vehiclematerial, a printed material used in planography). As the evaluationmethod, cannequin was put on the recorded surface and the surface wasrubbed with a load of 450 g, and then, abrasion and scratches on thecured surface of the recorded material were visually observed andcompared.

Evaluation criteria are as follows. The evaluation results are shown inTables 2 to 5.

1: No stains were observed. No abrasion or scratches were observed onthe printed surface.2: Strains on the cannequin were observed. No abrasion or scratches wereobserved on the printed surface.3: Strains on the cannequin were observed. Abrasion or scratches on theprinted surface were observed.

5. Bleed Resistance

Periphery portion of the obtained solid patterned image was visuallyobserved. Evaluation criteria are as follows. The evaluation results areshown in Tables 2 to 5.

1: Bleeding on the periphery portion of the solid patterned image wasnot observed.2: Bleeding on the periphery portion of the solid patterned image wasobserved.

6. Discharging Stability

An ink jet evaluating device (test model) having 180 nozzles in which adischarging nozzle diameter was set as 20 μm and a driving frequency wasset as 18 kHz, and an ink discharging amount for each time was adjustedto be 11 ng, was prepared. Using this evaluating device, the number ofnozzles in which nozzle omission occurred when continuously performingink discharging for 60 minutes was acquired.

Evaluation criteria are as follows. The evaluation results are shown inTables 2 to 5.

1: 1 nozzle or less2: 2 to 4 nozzles3: 5 nozzles or more

7. Glossiness

Glossiness at a turning angle of 60° C. was measured using a gloss meter(product name: MINOLTA MULTI GLOSS 268 manufactured by Knoica MinoltaSensing, Inc.).

Evaluation criteria are as follows. The evaluation results are shown inTables 2 to 5.

A: Equal to or more than 80B: Equal to or more than 70 and less than 80C: Equal to or more than 60 and less than 70D: Less than 60

TABLE 2 Examples 1 to 10 Example No. Item 1 2 3 4 5 6 7 8 9 10 Ink No. 11 1 1 1 1 1 1 1 1 Peak intensity 800 1500 3000 800 800 1500 — 1500 13001000 of first irradiation unit Irradiation energy 400 400 800 200 200100 — 400 173 400 Peak intensity — — — — 500 1500 1500 — — — of secondirradiation unit Irradiation energy — — — — 100 200 400 — — — Evaluationresults Cured wrinkles ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ Hardenability ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯◯ ◯ Abrasion resistance 1 1 1 1 1 1 1 1 1 1 Discharging stability 1 2 31 1 1 1 3 1 2 Bleeding resistance 1 1 1 1 1 1 2 1 1 1 Glossiness C B B CC B B B B B

TABLE 3 Examples 11 to 13 Example No. Example Item 11 12 13 Ink No. 4 56 Peak intensity of first irradiation unit 1000   1000   1000  Irradiation energy 400  400  400  Peak intensity of second irradiation —— — unit Irradiation energy — — — Evaluation results Cured wrinkles ◯ ◯Δ Hardenability ◯ ◯ ◯ Abrasion resistance 1 1 1 Discharging stability 22 2 Bleeding resistance 1 1 1 Glossiness B B C

TABLE 4 Comparative Examples 1 to 6 and Reference Examples 1 to 6Example No. Comparative Examples Reference Examples Item 1 2 3 4 5 6 1 23 4 5 6 Ink No. 1 1 1 1 1 1 2 2 2 3 7 8 Peak intensity 500 500 500 500100 500 500 800 1500 500 800 800 of first irradiation unit Irradiationenergy 200 100 200 100 1500 200 200 400 400 200 400 400 Peak intensity —800 800 — — — — — — — — — of second irradiation unit Irradiation energy— 400 400 — — — — — — — — — Evaluation results Cured wrinkles X X X ◯ XΔ Δ ◯ ◯ Δ ◯ Δ Hardenability ◯ ◯ ◯ X ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ Abrasion resistance2 1 1 3 1 2 1 1 1 1 1 1 Discharging stability 1 1 1 1 3 1 1 1 2 1 1 1Bleeding resistance 1 1 1 1 2 1 1 1 1 1 1 1 Glossiness D D D D D C B A AB A A

According to the results described above, it was clear that therecording method (Examples) including a discharging step of dischargingfirst ultraviolet curable ink of a radical polymerization reaction typewhich contains a radical photopolymerization initiator and a radicalpolymerization compound and in which transmittance at a wavelength of395 nm is equal to or less than 1%, onto a recording medium, and acuring step of curing the ink by setting the light source whichinitially irradiates the first ultraviolet curable ink which is landedon the recording medium with ultraviolet light as the UV-LED having thepeak intensity of the emitted ultraviolet light of equal to or more than800 mW/cm², can realize the excellent hardenability, efficiently preventthe cured wrinkles, and achieves excellent abrasion resistance,discharging stability, bleeding resistance, and glossiness, compared tothe other recording methods (Comparative Examples).

Supposition regarding the results described above are provided, however,the invention is not limited to the following supposition. According torespective Comparative Examples, it is found that the result of thecured wrinkles is poor and the glossiness is low, in a case where theirradiation peak intensity of the initial ultraviolet irradiation isless than 800 mW/cm². According to Comparative Example 1, it is assumedthat the abrasion resistance also tends to be degraded, in a case of thepoor result of the cured wrinkles. According to Comparative Example 5,it is assumed that the bleeding resistance tends to be degraded due tothe delay of curing by the first irradiation, in a case of extremelysmall irradiation peak intensity of the initial ultraviolet irradiation.

In addition, according to Example 2 and Comparative Example 5, in a casewhere the irradiation peak intensity of the initial ultravioletirradiation is extremely great or the irradiation energy thereof isextremely great, it is assumed that the discharging stability isdegraded since the change occurred in the discharging property with thesignificant degradation of the viscosity of the ink of the nozzle due tothe heat generation of the light source, or the polymerization of theink of the nozzle occurred due to large amount of light leakage from thelight source and accordingly the viscosity of the ink is increased.Meanwhile, according to Example 6, it is assumed that the excellentdischarging stability is obtained by setting the irradiation energy ofthe initial ultraviolet irradiation (first irradiation) to be relativelysmall, and setting the irradiation energy of the second ultravioletirradiation (second irradiation) to be relatively large.

In addition, according to Example 5, it is assumed that the curedwrinkles can be effectively prevented with any conditions of the secondultraviolet irradiation (second irradiation), in a case where theirradiation peak intensity of the initial ultraviolet irradiation (firstirradiation) is equal to or more than 800 mW/cm². According to Example7, it is assumed that the bleeding resistance tends to be degraded in acase of not performing irradiation by the first irradiation unit.

In addition, when comparing Examples 2 and 8, it is assumed that, in acase of using the LED with no lens, since the input current of the lightsource is necessary to be large and as a result, the heat generationbecomes great, the discharging stability tends to be degraded. Accordingto Example 9, it is assumed that the excellent discharging stability isobtained if the LED with no lens which is the LED with the pulseirradiation is used.

In addition, according to Comparative Example 6, in a case of using theserial printer, although the irradiation peak intensity was small, thegeneration of the cured wrinkles was suppressed compared to the case ofusing the line printer, however, recording could not be performed in ahigh speed.

Examples 14 to 23 and Comparative Example 7

In Examples 14 to 23 and Comparative Example 7, the ink jet recordingwas performed using an ink set obtained by combining the plurality ofink prepared as described above, and evaluations were performed.Hereinafter, Examples 14 to 23 and Comparative Example 7 will bedescribed in detail.

Ink Jet Recording

The ink jet recording was performed as disclosed in Table 5, by usingthe line printer shown in FIG. 2. The magenta ink head M (hereinafterreferred to as a “head M”) is filled with the ink to be previouslydischarged, and the yellow ink head Y (hereinafter referred to as a“head Y”) is filled with the ink to be discharged later, and the firstirradiation units 42 d and 42 e and the second irradiation unit 44 areoperated to perform evaluation using the ink set. In addition, even ifthe head M and the head Y are filled with ink other than the magenta inkor yellow ink, there are no effects for evaluation results.

Evaluation Items 8. Uneven Brightness

When a pattern of ink to be initially discharged and a pattern of ink tobe discharged later are formed to be adjacent to each other, thedifference in shiny appearance between the patterns was visuallyevaluated.

Evaluation criteria are as follows. Evaluation results were shown inTable 5 below.

A: Difference in shiny appearance was not observed.B: Difference in shiny appearance was observed.

TABLE 5 Examples 14 to 23 and Comparative Example 7 Example• ComparativeExample No. Examples Com. Ex. Item 14 15 16 17 18 19 20 21 22 23 7 Inkto be initially 1 1 1 1 2 2 2 2 1 1 2 discharged (used in head M) Peakintensity of 800 800 800 800 500 500 500 500 1500 1500 500 firstirradiation unit 42d Irradiation enegy 400 400 400 400 200 50 50 50 100100 50 Ink to be discharged 2 2 2 3 1 1 1 1 2 2 1 later (used in head Y)Peak intensity of 500 800 1500 500 800 800 1500 1500 500 500 500 firstirradiation unit 42e Irradiation energy 200 400 400 200 400 400 400 10050 300 200 Peak intensity of — — — — — — — 1500 1500 — 1500 secondirradiation unit 44 Irradiation energy — — — — — — — 200 100 — 200Evaluation results of the ink to be previously discharged Cured wrinkles◯ ◯ ◯ ◯ Δ Δ Δ Δ ◯ ◯ Δ Hardenability ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ Abrasionresistance 1 1 1 1 1 1 1 1 1 1 1 Discharging stability 1 1 1 1 1 1 1 1 11 1 Bleeding resistance 1 1 1 1 1 1 1 1 1 1 1 Glossiness C C C C B B B BB B B Evaluation results of ink to be discharged later Cured wrinkles Δ◯ ◯ Δ ◯ ◯ ◯ ◯ Δ Δ X Hardenability ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ Abrasionresistance 1 1 1 1 1 1 1 1 1 1 2 Discharging stability 1 1 2 1 1 1 2 1 11 1 Bleeding resistance 1 1 1 1 1 1 1 1 1 1 1 Glossiness B A A B C C B BB B D Evaluation results of entire ink set Uneven brightness A B B A A AA A A A B

It was found that, if there is difference of 2 or more ranks in theevaluation results of the glossiness between each ink configuring theink set (for example, evaluation as A and evaluation as C), the unevenbrightness in a case of using the ink set tends to be degraded.According to Examples 14 and 17 to 23, it is found that it is possibleto reduce the uneven brightness by setting the irradiation peakintensity when initially irradiating the ink at which transmittance at awavelength of 395 nm is equal to or less than 1%, to be equal to or morethan 800 mW/cm², and setting the irradiation peak intensity wheninitially irradiating the ink at which transmittance at a wavelength of395 nm exceeds 1%, to be less than 800 mW/cm². Meanwhile, it is assumedthat, in Example 15 and 16 in which the irradiation peak intensity wheninitially irradiating the second ultraviolet curable ink is set to beequal to or more than 800 mW/cm², the result of the cured wrinkles ofthe first ultraviolet curable ink was excellent, however, the differencein shiny appearance between the pattern of the first ultraviolet curableink and the pattern of the second ultraviolet curable ink is large andthe uneven brightness was observed. In addition, from comparison ofExamples 14 and 16, it was found that, the second ultraviolet curableink which can obtain relatively excellent curing wrinkles even when theirradiation peak intensity at the time of initial irradiation is lessthan 800 mW/cm², is advantageous in a viewpoint of excellent dischargingstability of two ink, by setting the irradiation peak intensity at thetime of initial irradiation to be less than 800 mW/cm².

The ink to be previously discharged in Examples 19 to 23 are irradiated(first irradiation) with the minimum irradiation energy to not generatethe bleeding, and the ink to be previously discharged is furtherirradiated (second irradiation) with the irradiation for the ink to bedischarged later. Accordingly, it is found that the dischargingstability of the ink to be previously discharged is excellent, the inkis sufficiently irradiated with ultraviolet light so as to obtainsufficient hardenability by the later irradiation, and it is possible toreduce cost and size of the light source of the first irradiation. InExample 21 or 22, by further performing the irradiation by the secondirradiation unit 44 and performing sufficient curing, it is possible toreduce size of the head M, the head Y, and the first irradiation units42 d and 42 e which position to be relatively close to the heads, andthe periphery of the head where disposition of various devices such asthe ink supply device or the head driving device is necessary is clearedfor space. Thus, Example 21 or 22 is advantageous compared to Examples14 to 18 or Example 23. In addition, it is possible to position theirradiation unit 44 to be relatively separated.

In addition, since the case of irradiation with the irradiation peakintensity of equal to or more than 800 mW/cm² results in the case oflarge irradiation energy, in many cases, compared to the case ofirradiation with the irradiation peak intensity of less than 800 mW/cm²(particularly, in a case where the irradiation time T1 is fixed), asExamples 18 to 21, it is advantageous to discharge the ink havingtransmittance at a wavelength of 395 nm of equal to or less than 1% andto irradiate the ink with the irradiation peak intensity of equal to ormore than 800 mW/cm², later than discharging the ink the ink havingtransmittance at a wavelength of 395 nm of more than 1% and irradiatingthe ink with the irradiation peak intensity of less than 800 mW/cm²,since it is possible to irradiate the ink having transmittance at awavelength of 395 nm of more than 1% by the irradiation with theirradiation peak intensity of equal to or more than 800 mW/cm².

According to comparison of Examples 20 and 21, it is found that, whenperforming the second irradiation after the first irradiation havingsmall irradiation energy for the ink having transmittance at awavelength of 395 nm of equal to or less than 1%, it is possible tosuppress the heat generation of or heat leakage from the light source ofthe first irradiation, and further excellent discharging stability ofthe head is obtained.

Hereinafter, the embodiment of the second invention will be described inmore detail with reference to Examples, however, the embodiment islimited to only the following Examples.

Used Raw Material

Raw materials used for Examples and Comparative Examples are as follows.

Coloring Material

-   -   Microlith Black C-K (C.I. Pigment Black 7, product name,        manufactured by BASF, hereinafter referred to as a “black        pigment”)

Dispersant

-   -   Solsperse 36000 (product name, manufactured by Lubrizol        Corporation, hereinafter referred to as “SOL 36000”)

Vinyl Ether Group-Containing (Meth)acrylate Esters

-   -   VEEA (2-(2-vinyloxy ethoxy) ethyl acrylate, product name,        manufactured by Nippon Shokubai Co., Ltd., hereinafter referred        to as “VEEA”)

Other Polymerization Compounds

-   -   Viscoat #192 (phenoxyethyl acrylate, product name, manufactured        by OSAKA ORGANIC CHEMICAL INDUSTRY LTD., hereinafter, referred        to as “PEA”)    -   IBXA (isobornyl acrylate, product name, manufactured by OSAKA        ORGANIC CHEMICAL INDUSTRY LTD., hereinafter, referred to as        “MX”)    -   V #160 (benzyl acrylate, product name, manufactured by OSAKA        ORGANIC CHEMICAL INDUSTRY LTD., hereinafter, referred to as        “BZA”)    -   SR 230 (diethylene glycol diacrylate, product name, manufactured        by Sartomer Company Inc., hereinafter, referred to as “DEGDA”)    -   APG-200 (tripropylene glycol diacrylate, product name,        manufactured by SHIN-NAKAMURA CHEMICAL CO., LTD., hereinafter,        referred to as “TPGDA”)

Photopolymerization Initiators

-   -   IRGACURE 819 (product name, manufactured by BASF, solid content        of 100%, hereinafter, referred to as “819”)    -   DAROCURE TPO (product name, manufactured by BASF, solid content        of 100%, hereinafter, referred to as “TPO”)

Slip Agent

-   -   BYK-UV3500 (product name, manufactured by BYK, hereinafter,        referred to as “UV3500”)

Examples 1 to 18 and Comparative Examples 1 to 11 Manufacture of PigmentDispersion Liquid

A pigment dispersion liquid was manufactured before manufacturing theink. 1.7 parts by mass of the black pigment, 0.6 parts by mass ofdispersant, and 20 parts by mass of polymerization compound as adispersion medium, were mixed, and stirred with a stirrer for 1 hour.The mixed liquid after stirring was dispersed with a bead mill, andpigment dispersion liquid was obtained. In addition, as dispersionconditions, zirconia beads having a diameter of 0.65 mm were filled witha filling rate of 70%, a circumferential speed was set to be 9 m/s,dispersion time was set to be 2 to 4 hours. The dispersion medium wasused with the polymerization compounds which can be used for each ink,in priority order of PEA, BZA, IBX, and VEEA.

Manufacture of Ultraviolet Curable Ink

Components disclosed in Table below were added to have compositionsdisclosed in Table below (unit is % by mass) and were stirred by ahigh-speed water-cooling type stirrer, and thus, ultraviolet curableblack ink 1 to 10 were prepared.

TABLE 6 Ink 1 to 10 Ink 1 Ink 2 Ink 3 Ink 4 Ink 5 Ink 6 Ink 7 Ink 8 Ink9 Ink 10 VEEA 25.0 65.0 — 74.5  25.0 25.0 10.0 35.0 — — PEA 30.0 10.035.0 5.0 — — 35.0 49.5 — — BZA — — — — 30.0 — — — 35.0 — IBX — — — — —30.0 — — — 35.0 DEGDA 20.0 5.0 40.0 5.0 20.0 20.0 25.0 2.5 40.0 40.0TPGDA 14.5 9.5 14.5 5.0 14.5 14.5 19.5 2.5 14.5 14.5 Black pigment 1.71.7 1.7 1.7 1.7 1.7 1.7 1.7 1.7 1.7 SOL 36000 0.6 0.6 0.6 0.6 0.6 0.60.6 0.6 0.6 0.6 819 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 TPO 4.0 4.04.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 UV 3500 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.20.2 0.2 Total 100.0 100.0 100.0 100.0  100.0 100.0 100.0 100.0 100.0100.0 Ink hardenability A A C A A B B B C C

Ink Jet Recording of Example 1

Ink jet recording was performed using the printer 1 which is a lineprinter in FIG. 4 described above. In detail, the black head K of theprinter 1 was filled with each ultraviolet curable ink prepared asdescribed above, respectively. Nozzle density of the head was set to be720 dpi. A solid patterned image having a film thickness of 10 μm wasprinted on a PET film (product name: PET 50A, manufactured by LintecCorporation) which is a recording medium, with conditions of recordingresolution of 720 dpi×720 dpi, Duty of 100%, and one pass (single pass).The printing was performed by heating each ink so that the viscosity ofthe ink is 10 mPa·s. In addition, the “solid patterned image” in thepresent specification means an image on which dots are recorded withrespect to all pixels each of which is a minimum recording unit areaspecified by the recording resolution.

With the recording, in order to cure the image, ultraviolet light havingirradiation peak intensity of 800 mW/cm² (see Table below), inputcurrent of LEDs of 120 mA (for each UV-LED), and a light emitting peakwavelength of 395 nm was emitted for predetermined time, from thelens-attached LED (described above) in the ultraviolet irradiationdevice installed on downstream of the recording medium in thetransportation direction, that is, the first irradiation unit 42 b. Theirradiation energy at that time was 400 mJ/cm² (see Table below).Accordingly, the ink jet recording was performed, and a recordedmaterial was obtained.

In addition, the irradiation peak intensity of each Example which willbe described later were adjusted by changing the input current of theLED elements, and were measured with a distance from a light emittingsurface to the recording medium. Further, the irradiation energy is avalue calculated from the sum of the irradiation peak intensity [mW/cm²]and the irradiation time [s]. In the printing, each irradiation unit 42and 44 continued irradiation, and the irradiation duration when onepoint from the irradiated surface of the recording medium which istransported under the irradiation units passes the irradiation areairradiated by the irradiation units were set as the irradiation time T1.The irradiation time T1 was adjusted by changing the number of theUV-LEDs which emit light from the plurality of UV-LEDs arranged in thetransportation direction of the recording medium in the irradiationunit. Other unit heads and irradiation units were not used.

Ink Jet Recording of Examples 2, 3, 7, 9, 10, and 13 to 18 andComparative Examples 1, and 3 to 11

The ink jet recording was performed in the same manner as Example 1except for setting the irradiation peak intensity and the irradiationenergy as values disclosed in Table below, and a recorded material wasobtained.

Ink Jet Recording of Example 8

The ink jet recording was performed in the same manner as Example 1except for using the second irradiation unit 44 instead of the firstirradiation unit 42 b and setting the irradiation peak intensity and theirradiation energy as values disclosed in Table below, and a recordedmaterial was obtained.

Ink Jet Recording of Examples 4 to 6 and Comparative Example 2

The ink jet recording was performed in the same manner as Example 1except for setting the irradiation peak intensity and the irradiationenergy of the first irradiation unit 42 b as values disclosed in Tablebelow, using the second irradiation unit 44 in addition to the firstirradiation unit 42 b, and setting the irradiation peak intensity andthe irradiation energy thereof as values disclosed in Table below, and arecorded material was obtained.

Ink Jet Recording of Example 11

The ink jet recording was performed in the same manner as Example 1except for setting the LED in the first irradiation unit 42 b as the LEDwith no lens described above instead of the lens-attached LED, and arecorded material was obtained. The irradiation time T1 was the same asExample 1. The input current of the LED was necessary to be 140 mA.

Ink Jet Recording of Example 12

The ink jet recording was performed in the same manner as Example 1except for using the LED with no lens which is the pulse irradiation LEDinstead of the lens-attached LED for the LED in the first irradiationunit 42 b and using the ink 2, and a recorded material was obtained. Inthe pulse irradiation LED, the Duty ratio was set to 0.5, the pulsefrequency was set to 1 kHz, and the input current was set to 220 mA. Theirradiation time T1 was the same as Example 1.

Evaluation Items

For the recorded materials obtained in respective Examples andComparative Examples, hardenability, cured wrinkles, abrasionresistance, bleed resistance, and discharging stability were evaluatedwith the following methods.

1. Hardenability Test 1

After rubbing the surface of the obtained solid patterned image(recorded surface) using a Johnson cotton swab manufactured by Johnson &Johnson, with 20 times of reciprocation and a load of 100 g, it wasdetermined whether or not there were scratches on the recorded surface,and the hardenability at the time of the printing was evaluated.Evaluation criteria are as follows. The evaluation results are shown inTable below.

O: No scratchesX: Scratches generated

2. Hardenability Test 2

When obtaining a cured coating film having a thickness of 10 μm byfurther coating the PET film (PET 50A) with each ink composition by abar coater and curing by emitting light by the UV-LED having theirradiation peak intensity of 800 mW/cm² and the light emitting peakwavelength of 395 nm, the surface was rubbed with the conditions same asHardenability Test 1, and irradiation energy necessary to have “0” ofthe evaluation criteria was evaluated. The evaluation results were shownin Table described above as “ink hardenability”.

A: Equal to or less than 200 mJ/cm²B: More than 200 mJ/cm² and equal to or less than 300 mJ/cm²C: More than 300 mJ/cm²

3. Cured Wrinkles

For surface roughness of the recording medium, a root mean square height(Rq value) was measured by using a laser microscope VK-9700(manufactured by KEYENCE), and the recorded surface was visuallyobserved.

Evaluation criteria are as follows. The evaluation results are shown inTable below.

O: Rq was equal to or less than 3. Sufficient shiny appearance wasobserved when seen reflected light of the film.Δ: Rq exceeded 3 or was equal to or less than 5. Slightly insufficientshiny appearance was observed when seen reflected light of the film.X: Rq exceeded 5. Shiny appearance was insufficient and the surface wasobserved to be rough when seen under the reflected light of the film.

4. Abrasion Resistance

Evaluation of abrasion resistance was performed using a Color FastnessRubbing Tester (manufactured by TESTER SANGYO CO., LTD.), based on JISK5701 (ISO 11628) (regulation of a method for testing ink, a vehiclematerial, a printed material used in planography). As the evaluationmethod, cannequin was put on the recorded surface and the surface wasrubbed with a load of 400 g, and then, abrasion and scratches on thecured surface of the recorded material were visually observed andcompared.

Evaluation criteria are as follows. The evaluation results are shown inTable below.

1: No stains were observed. No abrasion or scratches were observed onthe printed surface.2: Strains on the cannequin were observed. No abrasion or scratches wereobserved on the printed surface.3: Strains on the cannequin were observed. Abrasion or scratches on theprinted surface were observed.

5. Bleed Resistance

Periphery portion of the obtained solid patterned image was visuallyobserved. Evaluation criteria are as follows. The evaluation results areshown in Table below.

1: Bleeding on the periphery portion of the solid patterned image wasnot observed.2: Bleeding on the periphery portion of the solid patterned image wasobserved.

6. Discharging Stability

An ink jet evaluating device (test model) having 180 nozzles in which adischarging nozzle diameter was set as 20 μm and a driving frequency wasset as 18 kHz, and an ink discharging amount for each time was adjustedto be 11 ng, was prepared. Using this evaluating device, the number ofnozzles in which nozzle omission occurred when continuously performingink discharging for 60 minutes was acquired.

Evaluation criteria are as follows.

The evaluation results are shown in Table below.1: 1 nozzle or less2: 2 to 4 nozzles3: 5 to 7 nozzles4: 8 nozzles or more

TABLE 7 Examples 1 to 12 Example No. Item 1 2 3 4 5 6 7 8 9 10 11 12 InkNo. 1 1 1 1 1 1 1 1 2 2 1 2 Peak intensity 800 1500 3000 500 500 800 800— 800 1500 800 1300 of first irradiation unit Irradiation energy 400 400800 20 50 150 200 — 400 400 400 325 Peak intensity — — — 800 800 1500 —1500   — — — — of second irradiation unit Irradiation energy — — — 400400 250 — 400  — — — — Evaluation results Cured wrinkles ◯ ◯ ◯ ◯ Δ ◯ ◯ ◯Δ ◯ ◯ ◯ Hardenability ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ Abrasion resistance 1 1 11 1 2 1 1 1 1 1 1 Discharging stability 1 2 3 1 1 1 1 1 1 2 2 1 Bleedingresistance 1 1 1 1 1 1 1 2 1 1 1 1

TABLE 8 Examples 13 to 18 Example No. Item 13 14 15 16 17 18 Ink No. 2 45 6 7 8 Peak intensity 1000 1500 1500 1500 1500 1500 of firstirradiation unit Irradiation energy 400 400 400 400 400 400 Peakintensity — — — — — — of second irradiation unit Irradiation energy — —— — — — Evaluation results Cured wrinkles ◯ Δ ◯ ◯ ◯ Δ Hardenability ◯ ◯◯ ◯ ◯ ◯ Abrasion resistance 1 1 1 1 1 2 Discharging stability 2 2 2 3 22 Bleeding resistance 1 1 1 1 1 1

TABLE 9 Comparative Examples 1 to 11 Example No. Item 1 2 3 4 5 6 7 8 910 11 Ink No. 1 1 1 1 1 2 3 3 9 10 3 Peak intensity 500 500 500 500 100500 500 800 800 800 500 of first irradiation unit Irradiation energy 45080 200 50 1500 200 200 200 200 200 600 Peak intensity — 790 — — — — — —— — — of second irradiation unit Irradiation energy — 600 — — — — — — —— — Evaluation results Cured wrinkles X X X ◯ X X ◯ ◯ ◯ ◯ ◯Hardenability ◯ ◯ ◯ X ◯ ◯ X X X X ◯ Abrasion resistance 2 2 2 3 2 2 3 33 3 1 Discharging stability 1 1 1 1 3 1 1 1 1 2 4 Bleeding resistance 11 1 1 2 1 2 2 2 2 1

According to the results described above, it was clear that theultraviolet curable ink containing predetermined vinyl ethergroup-containing (meth)acrylate esters are excellent in hardenability,and the recording method (Examples) including a discharging step ofdischarging the ink onto the recording medium, and a curing step ofcuring the ink which is landed on the recording medium by irradiatingthe ink with ultraviolet light from an ultraviolet light emitting diodein which peak intensity is equal to or more than 800 mW/cm², can realizethe excellent hardenability, efficiently prevent the cured wrinkles, andachieves excellent abrasion resistance, discharging stability, bleedingresistance, and glossiness, compared to the other recording methods(Comparative Examples).

Supposition regarding the results described above are provided.According to Comparative Example 1, it is assumed that the abrasionresistance also tends to be degraded, in a case of the poor result ofthe cured wrinkles. According to Example 5 and Comparative Example 2, itis assumed that, even in a case of performing the second irradiation,when the irradiation peak intensity of the first irradiation is lessthan 800 mW/cm², the results of the cured wrinkles are influenced. It isassumed that the poor result of the bleeding resistance in ComparativeExample 5 is because of the delay of the curing by the firstirradiation. According to Comparative Examples 3, 7, 8, and 11, it isassumed that the predetermined vinyl ether group-containing(meth)acrylate esters contained in the ink are excellent inhardenability and excellent bleeding resistance is obtained due toincrease of the curing speed, and it is also assumed that the curedwrinkles state is excellent as long as the irradiation energy is set tobe grate and the printing hardenability is excellent, even in a case ofcontaining the predetermined vinyl ether group-containing (meth)acrylateesters in the ink. In addition, Comparative Example 11 is not preferablesince extremely large amount of UV-LEDs to be arranged in thetransportation direction of the irradiation unit 42 b is necessary, andalso it is assumed that the heat generation is great due to the largenumber of UV-LEDs.

In addition, according to Examples 3 and 11, it is assumed that, whenthe irradiation peak intensity and the irradiation energy of the firstirradiation is extremely great, the discharging stability is degradedsince the change occurred in the discharging property with thesignificant degradation of the viscosity of the ink of the nozzle due tothe heat generation of the light source, or the polymerization of theink of the nozzle occurred due to large amount of light leakage from thelight source and accordingly the viscosity of the ink is increased.According to Example 8, it is assumed that the bleeding resistance tendsto be degraded in a case of not performing irradiation by the firstirradiation unit. According to Examples 9, 10, and 14, it is assumedthat, in a case of large amount of predetermined vinyl ethergroup-containing (meth)acrylate esters contained in the ink, the curedink tends to be slightly generated, however, it is possible toeffectively prevent the generation of the cured wrinkles by setting theirradiation peak intensity of the first irradiation to be relativelylarge. When comparing Examples 1 and 11, it is assumed that, in a caseof using the LED with no lens, since the input current of the lightsource is necessary to be large and as a result, the heat generationbecomes great, the discharging stability tends to be degraded. Accordingto Example 9 and 12, it is assumed that, if the LED with no lens whichis the LED with the pulse irradiation is used, it is possible to reducethe heat generation of the LED by increasing the irradiation peakwavelength and decreasing the irradiation energy, and the excellentdischarging stability is obtained. In addition, in the ink 6 and 10, theinitiators tend to be difficult to be dissolved, and in Example 16 orComparative Example 10, it is assumed that the discharging stability isdegraded due to segregation of the initiator. It is assumed that thedegradation of the abrasion resistance in Example 18 is because of thedegradation of the abrasion resistance of the ink 8.

What is claimed is:
 1. An ink jet recording method comprising:discharging ultraviolet curable ink containing vinyl ethergroup-containing (meth)acrylate ester(s) expressed by the followingGeneral Formula (I) onto a recording medium, wherein: the ultravioletcurable ink contains other monofunctional (meth)acrylate other than thevinyl ether group-containing (meth)acrylate ester(s) expressed byGeneral Formula (I), and the other monofunctional (meth)acrylatecontains one or more of monofunctional (meth)acrylate having an aromaticring skeleton, or isobornyl(meth)acrylate; and curing the ultravioletcurable ink which is landed on the recording medium by irradiating theink with ultraviolet light from an ultraviolet light emitting diode inwhich peak intensity of the irradiated ultraviolet light is equal to ormore than 800 mW/cm²;CH₂═CR¹—COOR²—O—CH═CH—R³  (I) (in the formula, R1 represents a hydrogenatom or a methyl group, R2 represents a divalent organic residue having2 to 20 carbon atoms, and R3 represents a hydrogen atom or a monovalentorganic residue having 1 to 11 carbon atoms).
 2. The ink jet recordingmethod according to claim 1, wherein an irradiation energy ofultraviolet light emitted from the ultraviolet light emitting diode is100 mJ/cm² to 600 mJ/cm².
 3. The ink jet recording method according toclaim 1, wherein the irradiation from the ultraviolet light emittingdiode is at least any of pulse irradiation and spot irradiation by acondensing lens individually.
 4. The ink jet recording method accordingto claim 1, wherein peak intensity of the irradiated ultraviolet lightis in a range of 800 mW/cm² to 4000 mW/cm².
 5. The ink jet recordingmethod according to claim 1, wherein the ultraviolet light emittingdiode has a light emitting peak wavelength in a range of 360 nm to 420nm.
 6. An ultraviolet curable ink used for the ink jet recording methodaccording to claim
 1. 7. An ink jet recording apparatus which is usedwith the ink jet recording method according to claim
 1. 8. The ink jetrecording method according to claim 1, wherein peak intensity of theirradiated ultraviolet light is in a range of 800 mW/cm² to 2,000mW/cm².
 9. The ink jet recording method according to claim 1, wherein acontent of the vinyl ether group-containing (meth)acrylate estersexpressed by the following General Formula (I) is 35% by mass or lesswith respect to a total content of the ink.
 10. The ink jet recordingmethod according to claim 1, further comprising recording using a lineink jet recording apparatus including a line head having a length equalto or greater than a length corresponding to a width of a recordingmedium.
 11. The ink jet recording method according to claim 1, whereinthe content of the vinyl ether group-containing(meth)acrylate ester(s)expressed by the General Formula (I) is 10 to 50% by mass with respectto a total content of the ultraviolet curable ink.
 12. The ink jetrecording method according to claim 1, wherein the content of themonofunctional (meth)acrylate except for the vinyl ethergroup-containing(meth)acrylate ester(s) expressed by the General Formula(I) is 30 to 50 by mass with respect to a total content of theultraviolet curable ink.
 13. The ink jet recording method according toclaim 1, wherein the content of the bifunctional or more (meth)acrylateis 5 to 34.5 by mass with respect to a total content of the ultravioletcurable ink.
 14. The ink jet recording method according to claim 1,wherein the other monofunctional (meth)acrylate includes monofunctional(meth)acrylate including an aromatic skeleton.
 15. The ink jet recordingmethod according to claim 1, wherein the other monofunctional(meth)acrylate contains one or more of phenoxyethyl (meth)acrylate,phenoxy diethylene glycol (meth)acrylate, 2-hydroxy-3-phenoxypropyl(meth)acrylate, and benzyl (meth)acrylate.